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Dreaded ABS light! Please HELP!
Okay guy’s I posted about my ABS light a long time ago now and have finally got around to pulling out the computer and going through all the checks listed in the Service manual. My car is a 1994 it has a computer with the black sticker and no code light built in to it. So my issue is my ABS light is on from the moment you turn the key and never goes out until you switch off again!
I have worked through the various resistance and continuity checks in the 2 or 3 pages of the manual and each check turns up nothing. All results are good. Is the computer dead or is there something else I am missing that maybe not in the manual? I cannot seem to get the diagnosis mode to work and flash a code on the ABS warning light. If I jumper the terminals up front the light just stays on as it does all the time. Any thoughts please guys? Thank you Lee |
Have you checked the basics - the ABS fuse and relay good and getting power to the system?
Dale |
Hi Dale,
These are part of the tests in the manual.. I have checked all fuses in the engine bay, rear wiper works so presume that fuse is okay too. have had the valve and motor relay out and they click and open and close correctly when 12v applied to them. I have checked earths at the ECU plug, 12V main power feed at the ECU Plug, AC voltage from sensors at the plug by rotating each wheel, resistance of each sensor, continuity between ECU plug and black/white wire from Alternator. Voltage and earth at pump plugs and the continuity checks details at the pump plug and ECU plug in the FSM. Think that covers all checks I have done so far.. Any help or suggestions much appreciated. Trying to get a Spare ECU to check but so far only found one from a 1993 with blue label and code light built in. also not sure why I cannot read a code by jumping the diagnostic terminals under the bonnet. Seems a bit odd. Thank you Lee |
Look closely at your connectors. My issue turned out to be the main connector. Several pins had fried on it. Good luck.
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Hi David, Thanks for input.
Is that main connector at the ECU end or pump end? What am I looking for exactly. Black male or female pins?? How did you fix that? Re-doing terminals on either of the plugs would be no joke if I could even get hold of terminals in the first place! If that is the case then it will have to be bulb out and no more ABS. I will strip it out if and when I get around to it! I toyed with removing it anyway to get a bit more space under the hood! |
Was this a jap or pommy car? Mentioned it before I think, but there are incompatibilities with the S I to III cars that will result in the ABS not working if there is a mix and match between years, which might be a possibility buying a non-runner....you'd have to inspect all the white tags on the harnesses....hoping there still there and legible. If the DIY approach won't work, good auto sparkys should have an ABS scan tool if you can't bring anything up - not really cost effective to buy one. At desperation stage, might be time to get friendly with a local mazda dealer and see if they'll plug in their machine.
ECU FD31-67-650 or 03? |
Leeroy - I am speaking about one of the connectors for the ABS pump, not the ECU. I too had the ABS light on and we spent a bunch of time checking everything. Even swapped out the relays and then the ECU in the trunk, but nothing worked. We then unplugged the ABS pump and inspected the pins inside the plug and found 3 or so burnt pins and wires. Couldn't be seen unless you unplugged the unit. I wish I could remember which plug it was but I think it was a 10 or 12 pin one. It's one we couldn't find an OEM replacement for, so we had to rewire in a non-OEM one. Works great now.
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My car is a RHD Japanese import. I have not replaced any of the ABS components. Not to say someone else hasn't the ECU is a black label FD03-67-650 is the part number on it.
I will look at the plug again. All the continuity checks the manual asks for on that plug check okay? Was it the plug car side though? Or pump side? Manual is testing pump side I think. If I can work out where the pins go car side I could maybe continuity check that end. There is certainly nothing obvious looking in the plug but then I was probably not looking for burn marks when I had it apart before. The other plug is the big 2 pin power feed one. No way I would entertain re-wiring that lot right now.. I reckon best bet would be cut a plug from a good loom and use that if I have to go that road. Cheers Lee |
So I swapped out the ECU tonight for another. Turned key to position 2. Light stayed on. Balls! I have pulled the pump plug connector off and had a closer look again. Nothing i can see from looking in either side of the plug. What next. In my mind.. By swapping a new ecu. When I key on the light would go off until I drive if it was a wheel sensor issue? Or something the ecu would only detect if engine was on or car was moving. So must rule out a lot of things. Is there a fuse in the pump I read somewhere. No checks in the manual for this?
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It probably isn't much help, but my ABS light has been on for about 5 years and I never found the problem. Like yours it comes on the instant I turn on the key.
Now I will check my ABS pump connector pins as David suggests, don't think I've done that yet... it's been so long I forget everything I have done to unsuccessfully find the problem. As a side note, I haven't really missed having ABS, I just find the light somewhat distracting but eventually you start to not notice it. |
Seems. Like this is quite common... Yet no solutions other than Davids one which I cannot see in my plug. Bulb out I reckon.. Very annoying. Hate not doing it right.
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When I get my car back, I will post up pics of the connector in question. Should be next week. We checked literally everything on the car and replaced the relays and two wheel sensors. Did not fix the issue. Mazda does make an ABS tester box that hooks up to the system to diagnose these issues. You might want to call dealers to see if anyone still has one laying around. I found one for sale for under $100. Would offer it up but I gave it to Addicted Performance in Knoxville TN.
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Under the black plastic cover on the ABS pump itself is a relay and I THINK a fuse or something in there too. That may be worth a poke around.
Unfortunately (in a way) the ABS system on this car is fairly robust, most problems stem from damaged wheel speed sensors or goobered up wiring. There's just not a lot of troubleshooting to fall back on. Dale |
Dale, there are two relays in there, an ABS relay (NA23437A2) and a valve hydraulic unit relay (NA23437A3). They are both around $150 and neither worked for me. These were the first thing I replaced and it's worth a shot for Leeroy. As Leeroy replaced the ABS control unit, he can rule that out. If he checked the wheel sensors properly, then that's another no go as well. This leaves, as you point out, very little else on the system. My guess is still a wiring issue. I forgot where I saw the issue posted on the forum, but someone else pointed out that the pump connector is a known fault point. Water gets into it, causing corrosion, and in my case, a short as well. Couldn't tell this from a visual inspection with the connectors together. Had to unplug the connector and inspect the inside.
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Hi Lee,
Sorry to read about your ABS light problems. Have you verified that each wheel sensor is good? Were there any repairs to the wiring to each wheel sensor? Did you verify that no shorts exist between each sensor wire? These wires to the sensors are double shielded so don't forget to verify the shield components are isolated from one another. Treat each shield like a separate conductor. Refer to the wiring diagram on Pg Z-106 for location and pin readouts. When you talk about the ECU, are you referring to the ABS CPU or the proper ECU (car's engine computer)? This thread has some good advice about checking shielded wires on the ABS system, have you seen it? ABS Light Only When Car is Rolling Cheers, George |
Hi guys. Thanks for the. Support and feedback.. so just to run over here I am again so everyone is in the same page. I have followed the test/diagnosis procedure in the 1994 brake system manual. Car is a 1994 RHD Japan import. First of all I believe I have confirmed the pump relays are both good. I tested them open circuit across two pins and then with voltage apppied they click and circuit closes across another pins as manual describes. Only thing ai would say ai noticed different between the manual and readings I got was the coil circuit. Does not show. Continuous when I test across it. I check something later and had the same thing and believe that if there is resistance in the wires my tester won't bleep for continuity but will read a resistance across there instead to confirm there is a circuit. I assume this is normal and as the relays appear to function and open and close the switched side should not be the cause of my light? next I tested resitance on each wheel sensor. In spec. Then I check resistance of each speed sensor back at the abs ECU plug. In spec. Then I jacked the car and rotated each wheel and measured voltage of each sensor at the ecu plug. In spec. Seems wheels sensors and therefore any related wiring are also okay? i have checked all the grounds and both ends of the car as described in the manual and voltage reading and ecu plug, main pump plug and continuity between the black/white alternator wire and ecu plug. All fine. All fuses in the engine bay seem fine and rear wiper works so I assume no need to check that fuse? ihave checked the continuity of the pins at the main pump as manual suggests which covers most pins. All fine. Same at the ECU end. lastly I swapped the ECU. I half expected the light to go out and then come on when I started or drove the car.. as ai imagine a ecu new to the car to have no fault to start with. However. Turning ignition to pos2 and the light just stayed glowing. car has not been started or driven as it has a number of bits of bodywork missing right now.. but I cannot see it going off?! Maybe I need to se if there is a computer around.. Doe it plug into the ECU end to read faults and would that pick up wiring or plug issues like you had David. My plug looks fine.. was it quite clear to see looking into it or did you partially pull the plug apart for some reason. There is nothing at all obvious looking in either the male or female ends. Male pins look perfect and no sign of burns from the little you can see of th female ones. Plus most of these get tested. |
Lee,
Have any of the sensors been replaced before? Does it look like the wiring to/from the sensors were repaired? Did you check that each sensor wire is not shorted out to the shield? This will be different than checking for continuity between the sensor wire and the ABS CPU. According to the schematic on Pg Z-106, there are 2 ABS fuses. One 60A fuse in the engine bay and another one, 15A in the fuse box. The Rear Wiper fuse (10A) only provides power to the ABS CPU. Please double check the B1 (40A) fuse in the engine bay as well. On the ABS hydraulic unit, you should read the following resistance measurements: ABS Motor: Connector O-03 Pin R/Y to Chassis Ground = short (reading though motor) ABS Motor: Connector O-03 Pin B/L to Chassis Ground = Open ABS Motor Relay: Connector O-02 Pin L/O to Pin V = short (reading through coil) ABS Motor Relay: Connector O-03 Pin B/L to Pin R/Y = open Solenoid Valve Relay: Connector O-02 Pin B/L to Pin V = short (reading through coil) Solenoid Valve Relay: Connector O-02 Pin G/O to Pin B = short (must place Neg lead on Pin B and Pos lead on Pin G/O) Solenoid Valve Relay: Connector O-02 Pin G/O to Pin B = high resistance (must place Pos lead on Pin B and Neg lead on Pin G/O) - you are verifying the diode works here. Solenoid Valve Relay: Connector O-02 Pin W/R to Pin G/O = open (must place Neg lead on Pin W/R and Pos lead on Pin G/O) Solenoid (LF): Connector O-02 Pin B/W to Pin G/Y = short (reading through coil) Solenoid (RF): Connector O-02 Pin BR to Pin G/Y = short (reading through coil) Solenoid (Rear): Connector O-02 Pin Y/G to Pin G/Y = short (reading through coil) All Solenoids: Connector O-02 Pin B to Pins Y/G, G/Y, BR, B/W = short (reading through coil) All Solenoids: Connector O-02 Pin B/W to Pin G/Y = short (reading through coil) All Solenoids: Connector O-02 Pin G/O to Pins Y/G, G/Y, BR, B/W = short (reading through coil) (must place the Pos lead on Pin G/O and Neg lead on the others) - checking diode again. All Solenoids: Connector O-02 Pin G/O to Pins Y/G, G/Y, BR, B/W = high resistance (reading through coil) (must place the Neg lead on Pin G/O and Pos lead on the others) - checking diode again. Remember, there is a diode in line with the Solenoid Valve Relay and solenoids on the ABS Hydraulic unit. Polarity on your DMM must be observed otherwise you will go on a wild goose chase. Next disconnect Connector O-01 and verify that the shield wires are not shorted to the Sensor wire of each Speed Sensor. Check by this: Connector O-01 Pin 1G to Pin 1K = Open Connector O-01 Pin 1F to Pin 1U = Open Connector O-01 Pin 1Q to Pin 1O = Open Connector O-01 Pin 1P to Pin 1L = Open Note: If you read resistance other than an Open, disconnect each Speed Sensor, Connectors O-04, O-05, O-06, and O-07. Then, verify the outside shield is isolated from each Sensor wire: Connector Ground #12 to Connector O-01 Pin 1K = Open Connector Ground #12 to Connector O-01 Pin 1U = Open Now verify the outside shield is isolated from each inner shield wire: Connector Ground #12 to Connector O-01 Pin 1G = Open Connector Ground #12 to Connector O-01 Pin 1F = Open Note: Ground #12 is located on the bumper assembly, above the rear license plate frame (see Pg Z-107, bottom right corner). The reason for the inner & outer shield wires in the front is to prevent ignition coil interference with each front sensor wire. Please report any abnormalities. Cheers, George |
Hi George, what can I say.. thank you for such a detailed and thorough list. I really appreciated you taking the time to put all that down. I am know electronics whiz... in fact ai hate it! Because of problems like this. But I should be able to work through that nicely and note my results. Just to confirm the PIN numbers and plug details are from the 1994 FSM. Also where you ask to measure resitance this is instead of a normal continuity test to rule out resistance messing with meter readings. So as a resistance. I assume a short would read as 1 or will I always get a ohm value? Open presumable 0. Roughly what is classsed as high resistance where you state that for the diode I think it was. I was not aware of a second abs fuse internally. Do you know which it is? As I recall cover is in Japanese?! I have triple checked all the others in the bay including the extras you mention. All good. I have visually inspected all sensor wires and they look fine. Not checked for shorts yet so will follow everything you set out above and hope it turns something up! |
Lee,
In reference to measuring resistance, a short equals 0 Ohms. An open equals "infinite" ohms. Typically, meters will read "O/L" for infinite ohms. Do not check for continuity during these resistance checks. Continuity checks are usually used to check diodes. People often use the Continuity function while checking wires because it allows you to hear a tone. Dependent upon the meter, the continuity check doesn't display resistance values. Be aware that you will see some resistance value when reading across the solenoid coils but should be close to 0. Let's say anything under 10 Ohms is a good measurement. But please post all values on the checks listed above. The "higher resistance" I mentioned should be anything above 10 ohms but under O/L (typically in the Megohm range). Again, document your values, please. Yes, the reference I used was the wiring diagram from a 94 USDM FD. I'm sorry, but I don't know where the ABS fuse is located in the fuse box (foot well). It is a 15A blade fuse, typically blue in color. There should be a fuse block locater in the forum. Lastly, are you able to open the ABS CPU to inspect its internals? If so, I'm curious to see its innards. Cheers, George |
Lee,
When measuring the open circuit condition for the wiring (as stated above) you must disconnect each Wheel Speed Sensor. Measurements should read: Connector O-01 Pin 1G to Pin 1K = Open Connector O-01 Pin 1F to Pin 1U = Open Connector O-01 Pin 1Q to Pin 1O = Open Connector O-01 Pin 1P to Pin 1L = Open If you measure a short (0 Ohms) with the Wheel Speed Sensors disconnected then it would mean a problem with the affected wiring. When each Wheel Speed Sensor is connected, you should measure: Connector O-01 Pin 1G to Pin 1K = 0.8-1.2kOhm (800 - 1,200 Ohms) Connector O-01 Pin 1F to Pin 1U = 0.8-1.2kOhm (800 - 1,200 Ohms) Connector O-01 Pin 1Q to Pin 1O = 0.8-1.2kOhm (800 - 1,200 Ohms) Connector O-01 Pin 1P to Pin 1L = 0.8-1.2kOhm (800 - 1,200 Ohms) If you measure a short (0 Ohms) or an open (O/L or infinite Ohms) with the Wheel Speed Sensors connected then it would mean a problem with the affected wiring or sensor. See below to test each Wheel Speed Sensor. When each Wheel Speed Sensor is disconnected, there should be identical measurements at: Connector O-04 Pin R to Pin W = 0.8-1.2kOhm (800 - 1,200 Ohms) Connector O-05 Pin O to Pin Y = 0.8-1.2kOhm (800 - 1,200 Ohms) Connector O-06 Pin LG to Pin Y/L = 0.8-1.2kOhm (800 - 1,200 Ohms) Connector O-07 Pin R/W to Pin L = 0.8-1.2kOhm (800 - 1,200 Ohms) If the resistance for each Wheel Speed Sensor is out of spec then you will need to replace the affected sensor. How does the each Sensor Rotor's teeth look? This is located behind the wheel hub. Is it clean, free of debris, and all teeth present? Would you please post your results from this additional information? Cheers, George |
Thanks for the extra info.. I will try and start working through this tonight. Regarding the extra info in your latest posts.. Not kean on opening the ABS ECU unless straight forward. And I have tried two with the exact same results. So maybe leave that until last!
I have checked the wheel speed sensors as detailed here with results in spec. Quote" When each Wheel Speed Sensor is connected, you should measure: Connector O-01 Pin 1G to Pin 1K = 0.8-1.2kOhm (800 - 1,200 Ohms) Connector O-01 Pin 1F to Pin 1U = 0.8-1.2kOhm (800 - 1,200 Ohms) Connector O-01 Pin 1Q to Pin 1O = 0.8-1.2kOhm (800 - 1,200 Ohms) Connector O-01 Pin 1P to Pin 1L = 0.8-1.2kOhm (800 - 1,200 Ohms) If you measure a short (0 Ohms) or an open (O/L or infinite Ohms) with the Wheel Speed Sensors connected then it would mean a problem with the affected wiring or sensor. See below to test each Wheel Speed Sensor. When each Wheel Speed Sensor is disconnected, there should be identical measurements at: Connector O-04 Pin R to Pin W = 0.8-1.2kOhm (800 - 1,200 Ohms) Connector O-05 Pin O to Pin Y = 0.8-1.2kOhm (800 - 1,200 Ohms) Connector O-06 Pin LG to Pin Y/L = 0.8-1.2kOhm (800 - 1,200 Ohms) Connector O-07 Pin R/W to Pin L = 0.8-1.2kOhm (800 - 1,200 Ohms)"END QUOTE From memory the results were all circa 920 ohms. So I will check shielding as outlined and post up what I get. I have also checked the teeth and cleaned around them.. all look fine. Thank you Lee |
George is the man!
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Wow. It was freeezing out there tonight! Got stuck in though and made all the checks. I have a couple of differences but I think it might be to do with how my multimeter works and one instruction didn't quite make sense. so starting at the front all seems okay accept I noted a difference on the O2 connector tests for the diode. Where the notes above say I should see a short I get approx 8.0Mohms and where I should see a high resistance I see open circuit. However I noticed a diode symbol on my meter and read the manual. It stated I should see 0.5-0.8mv across one way and open circuit the other way if the diode was good. I rested in this mode and got 0.55mv and open circuit. So I assume the diode is good. next at the back this was where is did not make sense. The notes above say to check the pins which are across each wheel sensor and I should see an open circuit. However these are surely reading the speed sensor resistance when the sensor is connnected. So as such I get pretty even readings between each of 0.95-1.0 Kohms. It is open circuit if I set it to continuity test. I pulled off one of the easy to get to speed sensors and verified open circuit here. I also checked all the ground checks as you stated. I did that with sensors connected and again with the easy to get to one off. All open circuit. I caanot get to any ground under my bumper so I used the ground connector in the spare wheel well inside the car. I assume ground is ground though? I checked it was good first too! let me know if I need to recheck anything or what is next? I was quite hoping to find something but I don't think I have?! |
Lee,
Thanks for enduring the cold weather this evening and responding with some information. I'll be glad to explain & clarify the test points you recorded. Additionally, I use a printed schematic to annotate what you find so I may ensure no stone goes unturned. Rest assured, there is a method to my madness! 1. Did you find the 15A ABS fuse in your fuse box? Was it good? 2. When you recorded the Wheel Speed Sensor resistance at 920 Ohms, was that at each sensor connector AND at Connector O-01? --Basically, we are testing the wiring from the ABS CPU to each Wheel Speed Sensor as a whole and then separately. 3. I may not have articulated this previously, but when you measure values for the ABS Hydraulic Unit components such as the ABS Motor, Motor Relay, Solenoids, etc... you should be taking measurements from the Hydraulic Unit side of the connector. This checks the electrical components of the Hydraulic Unit. 4. When you tested the diode on the Hydraulic Unit, did you observe the correct polarity with the meter leads? That is, Black (Neg) lead on Connector O-02 Pin B and Red (Pos) lead on Connector O-02 Pin G/O? Again, this is on the Hyd Unit side. This verifies the wiring through the diode and Solenoid Valve Relay. --The 8 Megohm resistance does seem unusually high when the diode is forward biased and open (infinite Ohms) when reversed biased. However, I am glad that you used the continuity function and recorded the voltage. Did you hear the tone "beep" one way and no tone when you swapped the leads? 5. I also made one oversight on this check: the FSM wants to test the diode between Connector O-02 Pin G/O (Red or Pos Lead) and Pin G/Y (Black or Neg lead). --Please verify this measurement, if not done already. --You should see identical measurements as you noted in Item 4. 6. Next, I ask that you verify the wiring from the Hyd Unit to the ABS CPU. So plug in Connector O-02 and leave Connector O-03 disconnected. At Connector O-01 check: Connector O-01 Pin 1T to Pin AG = short (reading through ABS Motor Relay coil) Connector O-01 Pin AG to Pin 1R = short (reading through Solenoid Valve Relay Coil) Connector O-01 Pin 1C to Pin AB = short (reading through Solenoid L.F Coil) Connector O-01 Pin AH to Pin AB = short (reading through Solenoid R.F. Coil) Connector O-01 Pin AI to Pin AB = short (reading through Solenoid Rear Coil) Connector O-01 Pin 1C to Connector O-03 Pin R/Y = short (reading straight through wires only) 7. Ground is Ground. However, there are some instances when testing the physical location of a ground point has significant value. As you took resistance measurements at the rear of the car, using the car's chassis as ground is acceptable. 8. Could you please specify what Wheel Speed Sensor Pins you checked for Open circuits and which ones measured 920 Ohms? --This may be difficult however, please disconnect all wheel speed sensor connectors to verify the shields are isolated from the sensor wire. --This is also the perfect time to inspect each wheel sensor connector for any corrosion or other abnormalities such as wire kinks. --Ensure the outer shield is isolated from the inner shield on the front Sensor wires. 9. Reconnect Connectors O-02 and O-03, and all the Wheel Speed Sensor connectors (O-04, O-05, O-06, & O-07) after all other resistance measurements were recorded. Leave Connector O-01 disconnected. Set your DMM to V-AC (It may be represented with a "V" plus a Sine wave). I would like you to follow the checks in the FSM, Pg P-52, Step 3. Do this only when you verified the wiring from the Wheel Speed Sensors to the ABS CPU are good. You may also need a buddy to help spin each tire (tyre). --Follow the chart in the FSM. You should see 50-60mV (that's millivolts) for each Wheel Speed Sensor. 10. Verify that the Ground wires to the ABS CPU measure a short. Check at: Connector O-01 Pin 1D to Ground = Short Connector O-01 Pin 1S to Ground = Short Connector O-01 Pin AF to Ground = Short 11. Verify that the Ground wire to the Hyd Unit measures a short. Check at: Connector O-02 Pin B to Ground = Short 12. Lastly, reconnect all ABS system Connectors but leave Connector O-01 disconnected. --Turn the key to ACC. Wait 30 sec. Does the ABS light illuminate with Connector O-01 disconnected? --Turn the key to ON but do not start the car. Wait 30sec for light test to finish. Does the ABS light extinguish with Connector O-01 disconnected? Now, shut down the car and remove key from the ignition. Reconnect Connector O-01 then disconnect Connector O-02. --Turn the key to ACC. Wait 30 sec. Does the ABS light illuminate with Connector O-02 disconnected? --Turn the key to ON but do not start the car. Wait 30 sec for the light test to finish. Does the ABS light extinguish with Connector O-02 disconnected? Holy crap! This post took much longer to compose than anticipated! When posting a reply, would you please copy & paste the important bits with your measurements? This will help me keep track of all the tests. I apologize in advance if this makes you double or triple check certain components. I want to remove all doubts to what is good and bad. Do you see the method to my madness yet? ;) Cheers, George |
Originally Posted by David Hayes
(Post 12262481)
George is the man!
Thank you for the compliment! I just offer help when needed. Cheers, George |
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