Turbopleb

Hello, so long story short, im a new Mazda tech working with normal and sometimes very special cars (like this one), one of the cars we are selling is having some trouble with various systems, the car has a full nut/bolt restoration to some extent, and has been sitting for at least a year.

I've installed a new battery, and the main issue is that the airbag light is on. The steering wheel comes from a newer model Mazda with airbag, this has been tested and works by a local rotary guru who has done so several times.

The airbag light is on continuously from ignition on to engine running, no flashing. This tells me that the connection to the airbag module isn't working. I have not had the time to look into this yet.

The main issue I have is that the ABS light is also on after starting to roll the car, I started my diagnosis with the wheel speed sensors, I measured them at the ABS control unit, where all but right front measured 1kOhm. I had 0 resistance in that wire.

After diagnosing where the problem lies, I found the rusty connector under passenger side taillight which caused connection issues. After fixing this, the ABS light is permanently on when ignition on or car running, which is messing with my head.

I would greatly appreciate any tips for how to read what the ABS module is missing in terms of signal and such. Tomorrow after work I will continue to diagnose and check power to the module, oscilloscope test wheel speed sensors.

Basically I just need help understanding if there's any way the control modules of ABS and Airbag indicate what errors it has.

From what I understand the Airbag module shows blinking lights in the dash when there's an error, but the ABS I have not seen any info about.

Really a shame that we don't have the ABS testing computer, I believe it's been thrown out or gone missing.

gracer7-rx7

iTrader: (16)

the wires of the abs wheel speed sensor often get stretched and broken internally when people attempt to remove suspension parts and accidentally stretch the wiring. A new sensor with the integrated wiring usually fixes this.

i have no idea about the air bag system. Hopefully someone else can help. You should be able to find replacement parts in the classifieds here. I removed most of my air bag sensors and computers. I have some of the parts if needed.

Turbopleb

Absolutely, the sensors were new when renovated, and has good resistance all the way up to the ABS unit as per the original post. I will check them tomorrow with oscilloscope.

DaleClark

iTrader: (55)

Normally when the ABS light comes on when the car is moving that's a wheel speed sensor. It can also be the sensor isn't installed dead on - I had one on my car that was cockeyed in the hole and threw that error since it wasn't picking up the tone ring as it went by.

As-is, the airbag system is pretty hardy so there's not a lot of good troubleshooting documented on the system. Also I think the light only goes out once the car is running, not sure on that. Same may be for ABS.

Dale

Turbopleb

Correct, I am going to check them when rotating to make sure of that. The only thing I don't like about it is that the symptom changed after fixing the wheel speed sensor cable. At first it only had the ABS light when rolling and afterwards, but now it has it directly after engine start.

Both the lights are constantly on at the moment when ignition on, engine running, or rolling.

DaleClark

iTrader: (55)

Wonder if the repaired wires are shorting on each other? That would likely immediately throw the ABS light.

Dale

Turbopleb

The repaired section is very well isolated, the wires have no cross continuity, and have been load tested with a 12v bulb end to end.

DaleClark

iTrader: (55)

Have you disconnected the battery/held down the brake pedal for 20 seconds to clear the codes out? Don't know if that will help.

Most of the "easy" ways to fix the airbag/ABS requires the ancient and no longer available testers from Mazda. You may have to get the shop manual out and test resistance on individual circuits to find the problem. The hard part is the car was totally taken apart so it's really hard to say where the fault came in. These systems are both pretty sturdy that's why there's not a lot of troubleshooting out there. The only thing I've ever had to fix on the two systems in the many FD's I've worked on have been bad ABS sensors with faulty wiring.

Dale

Topolino

iTrader: (2)

Apologies if I might be misremembering a bit (since it has been awhile). But there is a computer module for the airbag system under the middle dash area (LHD...above and to the right of the accelerator pedal). Those tend to go bad over time so you may simply need to replace yours with a good working unit. I'd check directly w resident parts guru Fritz Flynn on the forum to see if he has any for sale.

Note: It took me a couple used units before my problem was solved so try and make sure you get a properly working unit should you decide to purchase elsewhere.

Turbopleb

Sadly the special equipment seems to no longer be available. I will continue to measure all pins at the ABS module to make sure it has all the signals or voltages it wants. While measuring the battery has always been disconnected to make sure I don't create any additional problems.

I will keep all of you updated if I find anything wrong with it.

Turbopleb

Now I have read the wheel sensors at the ABS computer with oscilloscope with perfect signals. I have checked the relays for the ABS motor and solenoid valve and they are OK. From what I can tell the only pins which have 12v on ignition is 1A aka rear wiper = OK. Problem still persists even after test drive at about 60kmh. Pin AA and 1V might also be 12v but maybe under engine running condition.

7krayziboi

iTrader: (15)

Don’t give up , almost there !

Turbopleb

Haha I simply can't give up, I'm the one paid to fix this

Currently waiting until tomorrow to see if the local rotary guy has spare modules for both ABS and Airbag, so we can test swap them. I can't see any useful diagnosis through checking wires for the Airbag, so I'll just give it a guess at this point since the light is supposed to blink if other codes are showing.

7krayziboi

iTrader: (15)

I read a thread not too long ago , about someone fixing his ABS light staying on.
After changing lots of parts, turn out the the ABS pump connector was the culprit this whole time.

**it was non-visible while disconnected*
is the important part I recall.

iirc , he unplugged the connector , to find the culprit pins.

————————-

I also read somewhere(don’t quote me)
that ABS sensors work by year ,and mismatch Component is a no go .

Edit:ABS pump connector .
Edit: Unplugged the connector

here is the thread I’m talking about :
https://www.rx7club.com/3rd-generati...-help-1124309/

Turbopleb

Thanks! Will have a look.

SpinningDorito

iTrader: (2)

Oh boy, the airbag module . If it's on continuously the module down by your gas peddle attached to the heater core is either missing, not plugged in, or has gone bad.

Here are the error codes for the airbag light copied from an older thread:

The module has been NLA for a long time. If you can even find it from Mazda they charge a fortune for it. The issue seems to be related to age so if you find a used one you may not have much luck either.

One thing to note, if you do find a good unit and it flashes out an error code I would write down the error code and not keep the unit connected. I believe if it runs enough times with an error it burns an internal fuse (which may or may not be replaceable if you want to solder it in) and you go back to the continuous light.

There are a few threads on here discussing the errors, and one or two where people walk through PCB component repairs that fixed their module.

Turbopleb

Yep, the light is on constantly. I'm currently waiting until Monday for both ABS and Airbag modules to arrive.

SpinningDorito

iTrader: (2)

Awesome. Let me know how it works out. I haven't been able to find a good working airbag module yet, but I think I might try replacing the capacitors and resistor fuse that I have seen fix it for others.

7krayziboi

iTrader: (15)

Update ?

Turbopleb

Currently waiting for the modules to arrive, haven't had time to do any work on it since the last update.

Turbopleb

To give a final conclusion, problem with ABS was fixed with replacing the module. Will take it apart at some point to trace faults and see what's wrong with it. Still waiting for airbag module.

DaleClark

iTrader: (55)

One down! That's interesting, it's uncommon as far as I know for the ABS modules to have errors.

Dale

Turbopleb

The stock one looks like it's been living on a sea bottom for 5 years compared to the one we replaced with, so there's a possible reason at least.

DaleClark

iTrader: (55)

Must have gotten wet, maybe the hatch was open in a thunderstorm or something. That would definitely explain a failure!

Dale