Pinpoint Test NN - Rear Axle Speed Sensor

Code 1229, 1237 Or 1260

Turn ignition off. Unplug ECU connector. Install Breakout Box (014-00322) with proper overlay. Raise and support vehicle. Check sensor tone ring for damage. Check sensor mounting for looseness. Repair as necessary.

Check Speed Sensor Output

Ensure 4WD vehicles are in 2WD mode. On all vehicles, start engine and allow rear wheels to rotate at engine idle speed. Set Rotunda Meter (105-00053) or equivalent, to frequency counter (Hz) setting. Measure and record frequency between breakout box pins No. 21 and 22. Change meter to A/C mV setting. Measure and record voltage output between breakout box pins No. 21 and 22. Ensure both measurements are recorded at same wheel speed. Determine sensor output in mV/Hz, by dividing A/C voltage reading by frequency reading. If sensor output is more than 6.0 mV/Hz, output at ECU indicates air gap and sensor signal are okay. Go to step 4). If sensor output is less than specified, sensor output at ECU is insufficient. Go to next step.

Check Output At Speed Sensor

Disconnect sensor connector at rear differential. Repeat step 2), but measure and record frequency between 2 pins of sensor component connector. Change meter to A/C mV setting. Measure and record voltage output between 2 pins of sensor component connector. Ensure both readings are measured at same wheel speed. Determine sensor output in mV/Hz, by dividing A/C voltage reading by frequency reading. If sensor output is more than 6.0 mV/Hz, output at ECU indicates air gap and sensor signal are okay. Go to next step. If sensor output is less than specified, replace sensor and recheck sensor output.

Check For Wiring Intermittents

If all previous steps have been performed, and problem still exists, condition may be wiring related. Closely inspect Red/Pink wire and Light Green/Black wire between sensor and ECU. Perform the INTERMITTENT DIAGNOSIS PROCEDURE . If condition still exists after intermittent diagnosis procedure is performed, go to next step. If problem is corrected, test drive vehicle.

Check If Steps Have Been Completed

If this step is not completed, replacement of any system component without being instructed to do so may not correct system fault. This step requires that a valid code be present, completion of all prior steps, and affected wiring integrity verified. If all previous steps have not been completed, return to last test step completed, and continue testing. If all prior steps have been completed, replace rear axle speed sensor and go to step 6). If condition still exists after completing step 6), replace ECU and repeat step 6).

Sensor Output Drive Test

Remove breakout box and adapter. Connect all components. Clear fault codes and cycle ignition key. Drive vehicle and complete at least one hard left and right turn. Travel over a rough road at steady speed. Perform one hard acceleration from a stop. At completion of test drive, check for fault codes. If SYSTEM PASS is set, repair is complete. If code other than Code 1229, 1237 or 1260 is set, go to appropriate pinpoint test. See the TROUBLE CODE DIRECTORY . If Code 1229, 1237 or 1260 still exists and ECU has been replaced, go to next step.

Possible Conditions Not Checked

This step assumes that wiring integrity has been verified and rear axle sensor and ECU have been replaced. The following is time consuming and should be performed only after all previous possibilities have been exhausted. Inspect Red/Pink wire and Light Green/Black wire between rear axle sensor and ECU. Check for chafing or any other damage that could cause an open or shorted condition. Repair wiring as necessary. If wiring is okay, inspect for excessive axle vibration, especially over rough road. Ensure rear axle is operating correctly. Repair as necessary. If code still exists, repeat step 5).