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1994 base rx-7
Here are the things I've already checked.
1. Ohm'd all the sensors at the wheel sensor connector (not abs CPU connector)
2. checked fuses and relays. (On and off the pump)
3. fixed a sheared wire connector (car harness side) that rubbed against the chassis a bit too long. ( repaired by solder, shrink wrap and weather seal)
The car is currently not road worthy so its on jack stands. This is what I noticed.
With the rear end up on stands, I've gone through the 1st and 2nd gear and this did NOT activate the abs light
With the front end up on stands, I spun the front passenger side wheel and that activated the ABS light. I turned off the car to clear the ABS light and spun the front driver side, and this also activated the ABS light.
Do you think the ABS cpu is reading the front speed sensors as a emergency brake situation when I'm spinning the front wheels independent of each other?
I will check ohm the sensor from the CPU wiring harness from within the trunk tonight after work. Since i have a 94, I think the ABS cpu has a diagnostic mode. Do i need the special tool to read the code or can I just ground the diagnostic and read the code from inside the cabin?
Could you further explain the repaired wire? Does it have a shield? If it does, how did you repair it? Do you have any photos of the wire repair?
When you tested the sensors, I would like to confirm:
1. Was the car's rear end raised in the air and the front wheels on the ground when you tested the rear wheel sensors?
2. Was the car's front end raised in the air and rear end on the ground when you tested the front wheel sensors?
3. At any time, did you test the wheel sensors with all 4 tires on the ground or all 4 tires in the air?
4. If you spun one rear wheel (same fashion as you tested the front) by hand would that turn on the ABS light?
5. What do you mean by the car not being road worthy - Is it more administrative (like no insurance/proper registration)? Can the car move and steer under its own power?
There is a way to enter the ABS diagnostic mode, refer to the FSM. I don't have it available, presently. I suspect that the ABS system may be fine...although it should have turned on when the rear wheels were spinning and front wheels stationary.
FWIW, the ABS light typically is on when the car is on a dyno. The system senses the rear wheels moving while the front wheels remain stationary. Once the rear wheels stop moving & power cycles, the ABS light turns off. I may be wrong about the power cycle so the light may go out when all 4 wheels stop - it's been a while since I noted my ABS function on a dyno.
What speed did you bring the car up to? As a safety precaution, I would strongly advise not testing the rear end with it on jack stands. The car could become unstable and cause the stands to drop out. Then *VROOOM* car goes through something. If you have access to a 4 post body lift, raise the wheels 1-2" off the floor then that would be a safer route to test the drive line.
Cheers,
George
Last edited by Gen2n3; 11-25-17 at 03:25 PM.
Reason: Grammar errors corrected.
It looks like the ABS unit cannot be tested unless using the Mazda specific ABS tester. I mistook the Air Bag System diagnostic module for the Anti-Lock Brake System module. The Anti-Lock Brake diagnostics begin on Pg P-38 of the FSM. My apologies for any confusion.
I think the ABS system is just getting confused with all 4 wheels not turning at the same time. In general, if the sensors are mechanically sound, installed properly with a proper air gap to the tone ring, and they ohm out properly, you're good with the sensors.
You'll need to drive the car to really know for sure, I don't think there's any way you can be certain about how it's working on jack stands in the garage.
the wire i repaired has shielding. However the break in the wire was right after the shielding. I had to peel back 2 inches the metal shielding to allow for soldering, heat shrink and additional (same gauge ) wiring.
I should correct myself during my testing phase.
When i was testing all the connectors, the car was completely off the ground.
When rotating the back wheels via the power of the engine and tranny as well as rotating the front wheels by hand, it was all done while car was completely lifted on jack stands.
BTW, thanks for the suggestion of the lift, I took a gamble to put it into gear and knew the dangers. I will probably invest into a quick jack or max jack later on.
This was the wiring that i repaired. I did not document the full repair via photographs unfortunately because i thought it was a straight forward wire repair.
I just finished ohm testing all the wheel sensors via the connector in the trunk by disconnecting it from the ABS CPU. I retested all the relays, checked all the possible fuses. Checked the 2 connectors on the abs pump for continuity of ground and continuity of power. All checked out per FSM
I rechecked the connector that Chuck suggested in an old thread stating the filmsy power wire on the abs pump unit itself. Everything was clean and and un-charred. i pushed and pulled on each one of the wires for possible loose connections.
I guess last thing to do as Dale mentioned is to take it out for a drive.
Thank you for confirming my suspicion about ABS testing.
****,
Glad to lend a hand and offer advice! Did you repair the shield around the ABS wires? If the shield is not properly repaired then it could lead to EMI (electromagnetic interference) of the center conductor(s). I have a story about such a repair but will save that for another time. Here is a video of how to repair shielded wire (shied repair starts around 10:30):
As Dale confirmed, proper testing of your ABS system should be done when the car can be driven. Unless you have the ABS tester in your hip pocket? lol Either way, I believe that the ABS system should function normally given the tests you already performed. Just make sure to repair the shield before you test it on the road!
Thanks! Should I extending the shielding past my repair? The original split in the cable began maybe an inch before the actual shielding but due to the compact area, and short wiring, I peeled back the wiring to expose more of the black and red wire. The wires on the connector has no shielding to begin with.
Based upon the photos, it looks like these wires were repaired before. It also looks like the prior repair may have neglected the shield. I cannot fully make it out because of the electrical tape. Either way, you have the perfect time to make the proper repair. Bear with my explanation as I am not aware of your electrical skills. I mean no insults with any simplified explanations. Please refer to the FSM, Pg P-53 for the ABS wiring diagram. It may seem confusing to the novice when reading this schematic. Basically, the front wheel sensors have a double shielded wire system and a single shielded wire system in the rear. Think of the shield as another wire that needs to be connected to chassis ground. Remember, the purpose of shielding a wire is to protect that wire's center conductor from outside interference. That outside interference could come from the car's radio, cell phone, hi voltage power lines, radar (police or other), etc... Another analogy of a shielded wire is similar to a knight wearing armor. The hard metal skin protects the knight's gooey insides from weapons. I digress; let's look at the schematic, specifically the Left Front ABS Wheel Speed Sensor (bottom left corner of Diagram O (Pg P-53).
The wires between connector O-04 and X-10 have a broken box that surrounds the 2 wires, one Red and one White wire. That broken box represents a braided shield sheath. Physically, the shield should be as close to each side of the connector as possible. Back to the schematic, that shield is connected (soldered) to a Grey wire that is also connected to a Black wire. That Black wire is part of connector X-10 which then goes to chassis ground through JC-13 at Common Ground Point 12.
Now, let's look at the wire pair (Red wire and White wire) above connector X-10. The Red wire connects to another Grey wire. That Grey wire is connected to a shield that protects the White wire running between connectors X-10 and O-01. Again, this shield should be as close to each side of connectors O-01 and X-10 as possible. For consistency, a Grey wire from the shield is connected to a Red wire from connector O-01 at Pin 1G of the ABS Control Unit.
This type of shielded wire system is a hybrid of a double shield system. An outer shield protects two wires in between O-04 and X-10 connectors. This outer shield is chassis grounded because the likelihood of outside interference is greatest with wire harnesses exposed through the wheel wells. However, one of those inner wires (Red wire) is another shield. That "inner shield" is the outer shield for the White wire in between X-10 and O-01 connectors. The White wire requires less shielding because the chassis would absorb most of the external emissions.
When making repairs to a shielded wire system, it is important to replace any missing shield segment that once surrounded the wire splice (of the center conductor). Some braided shields can be easily soldered together using the same electrical flux, solder, and a solder iron. Avoid using stainless steel braid for this type of repair. Only use shield material made for electrical systems.
Thanks for stating the problem was fixed. How did you fix the ABS light?
Cheers,
George
George, I just extended the wires and reconnected the the connector via solder and heat shrink. Our previous discussion about the shielding extension was going to be my second attempt to repair the connection if the ABS light was still on. I finally put the suspension, wheels and body panels back together so i could drive it around the block.
11-25-17, 02:39 PM
