Test K: DTC C1229/C1237 - Rear Axle Speed Sensor (Dynamic): Testing

NOTE: If no problems are found while testing sensor and circuits, check for intermittent conditions. See INTERMITTENT FAILURES under DIAGNOSIS & TESTING.

Turn ignition off. Connect NGS tester or scan tool. Turn ignition on. Retrieve DTCs. If DTC C1230 is retrieved, service DTC C1230 and ignore other DTCs. See TEST J . If DTC C1230 is not set, go to next step.
Using NGS tester, monitor ABCM PIDs LF_WSPD, RF_WSPD and R_WSPD. Drive vehicle at various speeds. If rear ABS sensor signal consistently matches front ABS sensor signals, condition is intermittent. Go to step 7. If rear ABS sensor signal is not consistent with front ABS sensor signals, go to next step.
NOTE: If a hard turn is made during test drive, some variation between all 3 sensors is expected. Rear speed signal should always fall between the left front and right front speed signals.
Raise and support vehicle. Rotate and carefully inspect sensor ring for damaged or missing teeth. If sensor ring is damaged, replace ring. Clear DTCs and road test vehicle on rough roads and through car wash. Recheck system operation. If sensor ring is okay, go to next step.
Check rear ABS sensor for looseness. If sensor is loose, tighten it. Clear DTCs and road test vehicle on rough roads and through car wash. Recheck system operation. If sensor is tight, go to next step.
Turn ignition off. Disconnect rear ABS sensor connector. Measure resistance between a known-good ground and both sensor terminals. If resistance is more than 10 k/ohms, go to next step. If resistance is less than 10 k/ohms, replace sensor. Clear DTCs and road test vehicle on rough roads and through car wash. Recheck system operation.
Turn ignition off. Disconnect ABCM. Install breakout box. Measure resistance between breakout box pins No. 6 and 14 (except late production Excursion), or No. 9 and 21 (late production Excursion). If resistance is more than 10 k/ohms, go to step 8. If resistance is less than 10 k/ohms, repair harness Light Green/Black and Red/Pink wire circuit(s) for short to each other. Clear DTCs and road test vehicle on rough roads and through car wash. Recheck system operation.
Problem may be intermittent. See INTERMITTENT FAILURES under DIAGNOSIS & TESTING. If rear ABS sensor passes intermittent test, go to next step. If it does not pass test, repair as needed. Clear DTCs and road test vehicle on rough roads and through car wash. Recheck system operation.
Turn ignition off. Remove rear ABS sensor. Inspect sensor for cracks or damage. Inspect wiring connector for debris, corrosion or water entry. If necessary, repair or replace. Clear DTCs and road test vehicle on rough roads and through car wash. Recheck system operation. If rear ABS sensor is okay, clear DTCs and road test vehicle on rough roads and through car wash. Recheck system operation.