Test G: Front Abs Sensor (Dynamic)

ABCM senses a missing, erratic or improper ABS sensor signal. DTC C1148/1234 or C1158/1233 will be generated when front ABS sensor indicates speed of 20 MPH or more with brakes applied, or vehicle speed is greater than 12 MPH and brake is released. DTC is generated when front ABS sensor signal is missing or low while other wheel speed sensors indicate a greater speed. Vehicle must be moving to set either DTC. With either DTC set, ABS warning light will illuminate and ABS will be disabled. Possible conditions include defective or damaged front ABS sensor, short or open in front ABS sensor circuit, incorrect air gap, axle vibration and defective ABCM.

1. Retrieve DTCs
   
   Turn ignition off. Connect scan tool. Turn ignition on. Retrieve continuous DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  S. If DTC C1145 or C1155 is retrieved, go to TEST F  . Ignore any other DTC retrieved. If either of these DTCs is not retrieved, but if DTC C1148, C1234, C1158 and/or C1233 is/are retrieved, go to next step. If any other DTC is retrieved, see DTC TEST INDEX  table to find appropriate test.
   NOTE: Recording all driving speeds for later plotting will eliminate need of monitoring scan tester while driving. If hard turn is made while driving, some variation between all sensors may be noted and is normal.
2. Repeatability Test Drive (Mismatched Output)
   
   With Scan tool, monitor ABS Parameter Identifications (PIDs), including LF_WSPI, LR_WSPI, RF_WSPI and RR_WSPI. Drive vehicle at various speeds and over rough roads. If suspect ABS sensor signal matches all other ABS sensor signals, check for an intermittent problem, and go to step 8)  . If suspect ABS sensor signal does not match all other ABS sensor signals, problem is repeatable. Go to next step.
3. Check Sensor For Internal Short
   
   Disconnect suspect ABS sensor connector. Using a DVOM, check resistance between sensor terminals and ground. If resistances are more than 10,000 ohms, go to next step. If resistances are less than 10,000 ohms, replace suspect ABS sensor, then go to step 10)  .
4. Check Suspect ABS Sensor For Open
   
   Check resistance between terminals of suspect ABS sensor connector (component side). If resistance is 2400-2800 ohms, go to next step. If resistance is not 2400-2800 ohms, replace suspect ABS sensor and go to step 10)  .
5. Check ABS Sensor Circuits
   
   Connect breakout box to ABCM harness. For right front, measure resistance between breakout box pins No. 53 and 55. For left front, measure resistance between breakout box pins No. 34 and 26. Then, measure between each pin and ground. If resistances for more than 10,000 ohms, go to next step. If resistances are less than 10,000 ohms, repair circuit(s) in question, then go to step 10)  .
6. Check Air Gap
   
   Raise and support vehicle. Check air gap of ABS sensor. See ABS SENSOR  under ADJUSTMENTS. See Figure . If air gap is .030-.050" (0.76-1.27 mm) air gap is okay, go to next step. If air gap is not as specified, replace ABS sensor, and/or repair or replace other loose or damaged components. Go to step 9)  .
7. Check Components
   
   It is necessary to make a careful inspection of all suspect or adjoining components. Remove suspect ABS sensor. Visually inspect sensor and harness for damage, corrosion and improper fit. If all components are okay, replace suspect ABS sensor and go to step 10)  . If damage is found, repair or replace as necessary and go to step 10)  .
8. Intermittent Diagnosis
   
   Conduct intermittent failure sensor failure test for suspect ABS sensor. See INTERMITTENT FAILURES  . If suspect ABS sensor passed intermittent failure test, reconnect sensor and go to step 10)  . If sensor did not pass intermittent failure test, go to next step.
9. Check Components (For Intermittent Test)
   
   Make a careful examination of all parts at this time to avoid wasted diagnosis time or unnecessary parts replacement. Remove suspect ABS sensor. Visually inspect sensor indicator, sensor and cable for any signs of wear or damage. If components are okay, go to next step. If necessary, repair or replace components as needed. Go to next step.
10. Verify Repair
    
    Reconnect and restore system. Clear continuous DTCs. Repeat DRIVE CYCLE TEST  . Retrieve and record any DTCs present. If SYSTEM PASS is obtained, go to next step. If SYSTEM PASS is not obtained and if original code is still retrieved, go back to step 2)  . If a different DTC is retrieved, go to DTC TEST INDEX  table to find appropriate test.
11. Verification Test Drive
    
    Test drive vehicle and record speeds for later plotting; this eliminates having to monitor Scan tool while driving. Note ABS Parameter Identifications (PIDs): LF_WSPI, LR_WSPI, RF_WSPI, and RR_WSPI. Gradually and smoothly accelerate from stop to 20 MPH several times. If suspect front ABS sensor signal consistently matches other sensor signals, repair is complete. If signals are mismatched, problem is repeatable. Go to step 3)  .