C1027 Left Rear Wheel Speed Sensor Signal Erratic Performance

C1027 Left Rear Wheel Speed Sensor Signal Erratic Performance - When the Left Rear Wheel Speed Sensor (WSS) signal is intermittently missing while vehicle speed is above 25 mph (40 km/h) or erratic wheel speed signal during acceleration or sensed wheel speed is different from other wheel.

C1027 Left Rear Wheel Speed Sensor Signal Erratic Performance

Possible Causes 

  • Left rear WSS loose circuit/connector/terminal damage.
  • Left rear tone wheel damage.
  • Left rear wheel/bearing damage.
  • Improper left rear tire pressure/mismatched tires.
  • Left rear WSS.
  • Antilock Brake System (ABS) Module.

Diagnose DTC C1027 Left Rear Wheel Speed Sensor Signal Erratic Performance


Step 1. Check for DTC C1027 Code
This DTC must be active for the results of this test to be valid. Turn the ignition on, with the scan tool erase DTC.

Caution: Make sure braking capability is available before road testing.

Road test the vehicle over 25 mph (40 km/h). Vehicle must be driven above 25 mph (40 km/h) for set conditions to be met. With the scan tool, read DTC.

Does the scan tool display DTC C1027 Left Rear Wheel Speed Sensor Signal Erratic Performance? 

YES, go to step 3.

NO, go to step 2.

Step 2. Check wheel speed sensor signals
Turn the ignition on, with the scan tool, monitor and graph all the WSS speeds and compare graph while an assistant drives the vehicle.
If graph shows periodic dropouts pay close attention to the tone wheel.
Slowly accelerate as staright as possible from a stop to 25 mph (40 km/h)

Is the left rear WSS speed showing 0 mph (0 km/h) or not matching other wheels or showing erratic behavior?

YES, go to step 3.

NO, perform the ABS Intermittent condition.

Step 3. Check for improper left rear tire pressure/mismatched tires
Turn the ignition off, check and adjust the left rear tire pressure. Check and adjust all other tire pressures, inspect for mismatched tires on vehicle.

Is the left rear tire improperly inflated or mismatched tires on vehicle?

YES, repair as necessary.

NO, go to step 4.

Step 4. Check axle shaft fastener hardware for looseness
Inspect the axle shaft fastener for looseness, and not properly fastened. Tighten fastener to proper specification as required.

Was the axle shaft fastener loose?

YES, repair as necessary.

NO, go to step 5.

Step 5. Check left rear WSS looseness, inspect circuits/terminals for damage
Check all terminals for broken, bent, pushed out, or corroded terminals.
Inspect the Antilock Brake System module harness connector, left rear WSS , and left rear WSS harness connector. Inspect the left rear WSS for looseness, excessive corrosion and not properly fastened. Inspect the left rear WSS signal and left rear WSS supply circuits between the left rear WSS and Antilock Brake System Module for damage.

Is the left rear WSS loose or any of the wiring/connectors/terminals damaged?

YES, repair as necessary.

NO, go to step 6.

Step 6. Check left rear wheel speed sensor for damage
Remove the left rear wheel speed sensor, inspect the left rear wheel speed sensor face for damage.

Is the left rear WSS damaged?

YES, replace sensor and hub assembly.

NO, go to step 7.

Step 7. Check left rear tone wheel/bearing for damage
Inspect the left rear tone wheel/bearing for damage, missing teeth, cracks, corrosion or looseness.
The tone wheel teeth should be perfectly square, not bent, or nicked.

Is the left rear tone wheel/bearing damaged?

YES, repair as necessary.

NO, go to step 8.

Step 8. Check left rear wheel bearing for damage
Inspect the left rear wheel bearing for excessive runout or clearance. Refer to the appropriate service information, if necessary, for procedures or specifications

Is the left rear wheel bearing damaged?

YES, repair as necessary.

NO, go to step 9.

Step 9. Left rear wheel speed sensor
Replace the left rear wheel speed sensor. Road test the vehicle over 25 mph (40 km/h). Vehicle must be driven above 25 mph (40 km/h) for set conditions to be met.

With the scan tool, read ABS DTC.

Did DTC C1027 Code reset?

YES, replace the Antilock Brake System (ABS) Module. Perform the ABS Verification Test.

NO, test complete for DTC C1027 Left Rear Wheel Speed Sensor Signal Erratic Performance.

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