My 99 STS kept illuminating the ABS and Traction control indicators, along with those indicators I would get the check stability system message. I just kept clearing them till I had the time to go through the system and find out why. The most common factor here is the Right Rear ABS sensor and its circuits. The codes were consistent and intermittent, they were:
DTC C1224 RR Wheel Speed Sensor Input Signal is 0
DTC C1228 RR Excessive Wheel Speed Variation
DTC C1235 RR Wheel Speed Circuit Open or Shorted
The ABS wheel speed sensor is self generating sensor, meaning it produces an AC signal or frequency that the brake module uses to calculate the wheel speed. There are other sensors that have the same operating principles such as in the engine control system, the camshaft and crankshaft sensors, in the transmission vss, and output shaft speed sensors.
So, you guessed it, I started at the right rear ABS sensor, I didn’t want to spend $400.00 just yet for a hub and sensor, so I checked out the circuits first, my suspicion and hope was that there’s a poor connection somewhere between the sensor and module.
I have a Tech2 so I drove the vehicle back and forth to work for several days, but, wouldn’t you know it, the car would never act up when the Tech2 was connected to the vehicle.
1. I measured the resistance of the right rear ABS sensor; I found the resistance @1k ohms, this is within specs 850-1350 ohms.
2. I then measure the AC signal frequency from the sensor; I set my DMM to the mV AC scale, and spun the wheel as fast as I could. The reading was over 110mV, this is within specs, it should be at least 100mV.
3. My suspicion along was a loose or poor connection some where between the RR sensor and brake module. So, then I started checking the terminal connections the first circuit I checked was 882 the brown terminal, I did what we call a terminal drag test and found very little drag resistance one that terminal compared to the other one. Upon a close inspection I found that the terminal was spread slightly, I reached in there with a small pick and closed up the gap.
4. Bada bing, bada boom, been driving the car for 3 days now, no problems, no lights.
DTC C1224 RR Wheel Speed Sensor Input Signal is 0
DTC C1228 RR Excessive Wheel Speed Variation
DTC C1235 RR Wheel Speed Circuit Open or Shorted
The ABS wheel speed sensor is self generating sensor, meaning it produces an AC signal or frequency that the brake module uses to calculate the wheel speed. There are other sensors that have the same operating principles such as in the engine control system, the camshaft and crankshaft sensors, in the transmission vss, and output shaft speed sensors.
So, you guessed it, I started at the right rear ABS sensor, I didn’t want to spend $400.00 just yet for a hub and sensor, so I checked out the circuits first, my suspicion and hope was that there’s a poor connection somewhere between the sensor and module.
I have a Tech2 so I drove the vehicle back and forth to work for several days, but, wouldn’t you know it, the car would never act up when the Tech2 was connected to the vehicle.
1. I measured the resistance of the right rear ABS sensor; I found the resistance @1k ohms, this is within specs 850-1350 ohms.
2. I then measure the AC signal frequency from the sensor; I set my DMM to the mV AC scale, and spun the wheel as fast as I could. The reading was over 110mV, this is within specs, it should be at least 100mV.
3. My suspicion along was a loose or poor connection some where between the RR sensor and brake module. So, then I started checking the terminal connections the first circuit I checked was 882 the brown terminal, I did what we call a terminal drag test and found very little drag resistance one that terminal compared to the other one. Upon a close inspection I found that the terminal was spread slightly, I reached in there with a small pick and closed up the gap.
4. Bada bing, bada boom, been driving the car for 3 days now, no problems, no lights.