[static///m3]

I recently restored a 91 turbo which had been sitting for years. The ABS light turns off after switching the car on. After I had flushed the brake fluid, I've noticed that when the brakes are cold, I can feel the ABS engaging when coming to a stop even at low speed. The pedal feels like it shudders and I hear the unit audibly.

What's strange is that after a few stops when driving (maybe 5-7) the brakes will feel fine. I'm guessing that the brakes have heated up at this point. The ABS no longer cuts in unexpectedly and the brake pedal feel is firm as if nothing is wrong.

Anyone have any ideas?

 

[mingtauw]

A few things to check that could cause this.

-Tire pressure are too low and/or unever across tires
-Tire tread wear is uneven across tires. (1 or more tires has significantly more wear). On MR2s, the resrs get worn quickly compared to the front. This can trigger ABS unnecessarily.

-What is the tire setup? Stock wheels and rims or aftermarket? If aftermarket what are the specs?

-If all this checks out, then its probably an ABS sensor. The rest of the system seems to be working correctly. Check the resistances of the sensors when cold, and then check them again warm. The resistance will change a bit, but all the sensors should be consistent with each other. The odd one out is probably bad.

Sent from my SM-G973U using Tapatalk

 

[static///m3]

A few things to check that could cause this.

-Tire pressure are too low and/or unever across tires
-Tire tread wear is uneven across tires. (1 or more tires has significantly more wear). On MR2s, the resrs get worn quickly compared to the front. This can trigger ABS unnecessarily.

-What is the tire setup? Stock wheels and rims or aftermarket? If aftermarket what are the specs?

-If all this checks out, then its probably an ABS sensor. The rest of the system seems to be working correctly. Check the resistances of the sensors when cold, and then check them again warm. The resistance will change a bit, but all the sensors should be consistent with each other. The odd one out is probably bad.

Sent from my SM-G973U using Tapatalk

I'm running aftermarket wheels and the tires are brand new. Setup up front is 17x8 215/40 and rear is 17x9 245/40.

The tire shop didn't ask me on tire pressure so I can double check that once I get off work.

 

[Alex W]

I would suspect a sensor. Check them for dirt on the tip, especially anything metallic stuck to them. It's a bit odd that there is a temperature effect (but if a sensor is just on the verge of failing I could see it), but magnetic debris on the sensor can definitely cause the sort of low speed false engagement that you are describing.

It's even one of the symptoms in the BGB. "ABS operates just before stopping at ordinary braking"

See page 58:

1991 MR2 BGB Online - Mechanical - Brake System

 

[static///m3]

I would suspect a sensor. Check them for dirt on the tip, especially anything metallic stuck to them. It's a bit odd that there is a temperature effect (but if a sensor is just on the verge of failing I could see it), but magnetic debris on the sensor can definitely cause the sort of low speed false engagement that you are describing.

It's even one of the symptoms in the BGB. "ABS operates just before stopping at ordinary braking"

See page 58:

1991 MR2 BGB Online - Mechanical - Brake System

So actually following through the testing of the sensors, I ran into two codes:
Code 74 - Diagnosis: Low voltage of rear left speed sensor signal - Malfunctioning Part: Rear Left speed sensor or sensor installation.
Code 76 - Diagnosis: Abnormal change of front left speed sensor signal - Malfunctioning Part: Front left sensor rotor or Front sealed wire.

For code 74, the sensor sits flush with the hub, no gap at all. I know for sure the tip was clean before inserting it, but it was taken from a previous parts car so I'm guessing the sensor itself is bad.
For 76, I'm not sure what the bgb is referring to for the "Front left sensor rotor" or "Front sealed wire."

 

[Alex W]

The sensor rotor would be the toothed wheel inside the knuckle. Unlikely to be bad, but possible I suppose. When Toyota wiring diagrams or manuals refer to a wire as being "sealed" what they really mean is shielded. Could be the shielding is somehow interrupted, causing the wire to pick up interference. Or it could just be a bad sensor on that corner as well. But I would double check that the sensors are clean first, as well as check everything else about the sensor and wiring that you can, before trying to replace them. They are hard to find replacements for and tend to be expensive, so you don't want to replace them unless you absolutely have to.

 

[static///m3]

The sensor rotor would be the toothed wheel inside the knuckle. Unlikely to be bad, but possible I suppose. When Toyota wiring diagrams or manuals refer to a wire as being "sealed" what they really mean is shielded. Could be the shielding is somehow interrupted, causing the wire to pick up interference. Or it could just be a bad sensor on that corner as well. But I would double check that the sensors are clean first, as well as check everything else about the sensor and wiring that you can, before trying to replace them. They are hard to find replacements for and tend to be expensive, so you don't want to replace them unless you absolutely have to.

Thanks Alex. I'll try to inspect the sensor up front tomorrow. I'm letting the mounting bolt soak overnight with penetrating fluid. Hopefully the bolt doesn't snap as I've had a hell of a time breaking so many other rusted fasteners during this things repair .