Has anyone seen a faulty skid control ECU in one of these?
I'm having a unique issue with trac in 4wd on my 2005 sequoia SR5.
The following situations are all when taking off from a stop going straight ahead.
In 4hi, taking off from a stop, the slip light flashes and power is cut momentarily. I'm definitely not having actual slip.
In 4hi with the center diff locked, this doesn't happen.
In 4lo with the center diff locked or unlocked, the trac system will actuate when taking off. I can feel it pulsating through the floor board and can hear it.
This issue is not happening in 2wd, and everything seems fine one the vehicle is moving.
Unplugging the level sensor on the master cylinder alleviates the problem.
It's done this since I bought it. Since then it's needed maintenance and I've completed
-new tires
-Rack and pinion + bushings + inner/outer tie rods
-LCA
-upper ball joint, lower ball joint
-Wheel bearings checked using shake test, no noise.
-removed and cleaned ABS sensors on each wheel, blew out the abs tone ring with compressed air
-brake fluid flushed, FR caliper replaced because the bleeder was seized and snapped off.
There are no codes in any module. Wheel speed sensors read the same speed when going straight.
This is the fsm trouble shooting flowsheet
Only when 1. to 9. are all normal and the problem is still occurring, replace the skid control ECU.
1. Check the DTC, reconfirming that the normal code is out put ----- check
2. Perform zero point calibration ---- check
3. IG power source circuit ----check
4. Check the hydraulic circuit for leakage --- check, no leaks
5. Speed sensor circuit ---- ??? see below
6. Deceleration sensor circuit
7. Yaw rate sensor circuit --- passed self test, live data shows it's working correctly.
8. Steering angle sensor circuit --- live data shows it's working
9. Master cylinder pressure sensor circuit --- passed self test
So assuming all this passes, replace skid control ECU.
I've put the vehicle in test mode and performed the following
--self test of yaw/decel (buzzer sounds when setting off and when stopped and vehicle is in park)
--brake pedal stroke/force sensor self test works (buzzer sounds when pushing pedal)
--steering angle is -1 to 1 straight ahead, and changes with more angle as it should
*****I can not get the vehicle speed sensor self test to work. After taking off from a stop and driving straight for 28+ mph for several seconds, I couldn't get the ABS light to quit flashing. I've tried twice. Perhaps because I had to maneuver from the parking lot to the road before beginning the test. However, I performed the brake test on the street and immediately drove straight after testing the brake sensor, without turning. And the ABS light did not stop flashing.
So going to the FSM flowsheet for the wheel speed sensor.
1. Check output value of speed sensor --- check, all agree when going straight. There is a difference when turning, which tells me they're actually working and there is no signal substitution (if that's even possible in the first place)
2. Check speed sensor --- check, resistance across sensor is good, resistance to ground is infinite.
3. Check for open and short circuit in harness and connector between each speed sensor and skid control ECU --- I checked at the skid control ecu, checks fine.
4. Check sensor installation --- check, all are fully seated in the bore
5. Check speed sensor and sensor rotor serrations --- no scope to check this, but no signal is dropping on live data
6. Check sensor rotor and sensor tip --- the tips had some junk. I blew the area out with compressed air. Drove the vehicle, issue persisted. Pulled sensor again, it was clean. The tone rings looks fine through the bore. Appear centered. Do not appear to slip on the hub when I apply pressure, runout looks good, no missing teeth. I'm not sure I want to buy a 20 ton press and specialty tools to push out the hub to check the front.
So now we're, again, at replace the skid control ECU.
I'm just finding it very doubful this is the issue with no trouble codes present, and only happening when taking off from a stop. Everything is pointing me towards a lag in wheel speed detection.
I'm having a unique issue with trac in 4wd on my 2005 sequoia SR5.
The following situations are all when taking off from a stop going straight ahead.
In 4hi, taking off from a stop, the slip light flashes and power is cut momentarily. I'm definitely not having actual slip.
In 4hi with the center diff locked, this doesn't happen.
In 4lo with the center diff locked or unlocked, the trac system will actuate when taking off. I can feel it pulsating through the floor board and can hear it.
This issue is not happening in 2wd, and everything seems fine one the vehicle is moving.
Unplugging the level sensor on the master cylinder alleviates the problem.
It's done this since I bought it. Since then it's needed maintenance and I've completed
-new tires
-Rack and pinion + bushings + inner/outer tie rods
-LCA
-upper ball joint, lower ball joint
-Wheel bearings checked using shake test, no noise.
-removed and cleaned ABS sensors on each wheel, blew out the abs tone ring with compressed air
-brake fluid flushed, FR caliper replaced because the bleeder was seized and snapped off.
There are no codes in any module. Wheel speed sensors read the same speed when going straight.
This is the fsm trouble shooting flowsheet
Only when 1. to 9. are all normal and the problem is still occurring, replace the skid control ECU.
1. Check the DTC, reconfirming that the normal code is out put ----- check
2. Perform zero point calibration ---- check
3. IG power source circuit ----check
4. Check the hydraulic circuit for leakage --- check, no leaks
5. Speed sensor circuit ---- ??? see below
6. Deceleration sensor circuit
7. Yaw rate sensor circuit --- passed self test, live data shows it's working correctly.
8. Steering angle sensor circuit --- live data shows it's working
9. Master cylinder pressure sensor circuit --- passed self test
So assuming all this passes, replace skid control ECU.
I've put the vehicle in test mode and performed the following
--self test of yaw/decel (buzzer sounds when setting off and when stopped and vehicle is in park)
--brake pedal stroke/force sensor self test works (buzzer sounds when pushing pedal)
--steering angle is -1 to 1 straight ahead, and changes with more angle as it should
*****I can not get the vehicle speed sensor self test to work. After taking off from a stop and driving straight for 28+ mph for several seconds, I couldn't get the ABS light to quit flashing. I've tried twice. Perhaps because I had to maneuver from the parking lot to the road before beginning the test. However, I performed the brake test on the street and immediately drove straight after testing the brake sensor, without turning. And the ABS light did not stop flashing.
So going to the FSM flowsheet for the wheel speed sensor.
1. Check output value of speed sensor --- check, all agree when going straight. There is a difference when turning, which tells me they're actually working and there is no signal substitution (if that's even possible in the first place)
2. Check speed sensor --- check, resistance across sensor is good, resistance to ground is infinite.
3. Check for open and short circuit in harness and connector between each speed sensor and skid control ECU --- I checked at the skid control ecu, checks fine.
4. Check sensor installation --- check, all are fully seated in the bore
5. Check speed sensor and sensor rotor serrations --- no scope to check this, but no signal is dropping on live data
6. Check sensor rotor and sensor tip --- the tips had some junk. I blew the area out with compressed air. Drove the vehicle, issue persisted. Pulled sensor again, it was clean. The tone rings looks fine through the bore. Appear centered. Do not appear to slip on the hub when I apply pressure, runout looks good, no missing teeth. I'm not sure I want to buy a 20 ton press and specialty tools to push out the hub to check the front.
So now we're, again, at replace the skid control ECU.
I'm just finding it very doubful this is the issue with no trouble codes present, and only happening when taking off from a stop. Everything is pointing me towards a lag in wheel speed detection.
