Diagnostic Aids

WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:
- A bent terminal
- A backed-out terminal
- A damaged terminal
- Poor terminal tension
- A chafed wire
- A broken wire inside the insulation
When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
You may have to drive the vehicle in order to experience a condition.
If the condition is intermittent, connect the scan tool and select the speed sensor indicated by the code. If the signal is erratic, investigate and eliminate the following:
- Intermittent wiring connection
- Excessive vibration, such as driveline or engine torsionals
- Irregular sensor gap, such as a loose sensor, a loose tone wheel or a damaged tone wheel
- Inspect that the speed sensor wiring consists of twisted pairs at the rate of 12-16 twists per 300 mm (12 in). These twists must extend the entire length of the wiring harness to within at least 50 mm (2 in) of the speed sensor connector.

Step	Action	Value	Yes	No
Schematic Reference: Automatic Transmission Controls Schematics
1	Did you perform the Diagnostic System Check - Vehicle?	-	Go to Step 2	Go to Diagnostic System Check - Vehicle
2	Install the scan tool. Turn ON the ignition, with the engine OFF. IMPORTANT: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data. Record the DTC Freeze Frame and Failure Records. Clear the DTC. Using the scan tool, observe ignition voltage. Is the voltage within the specified range?	9-18 V	Go to Step 3	Go to DTC P0562 for low voltage or DTC P0563 for high voltage
3	Turn the ignition OFF. Disconnect the 80-way connector at the TCM. Install the J 39700 breakout box, the J-47275 breakout box adapter and the J 47275-1 magnetic overlay. Using the DMM, measure the resistance between connector terminals 60 and 40. Is the speed sensor resistance within the specified value?	2WD: 2,600-3,160 Ω 4WD: 1,420-2,140 Ω	Go to Diagnostic Aids	Go to Step 4
4	Disconnect the wiring harness from the output speed sensor. Using the DMM and the J 35616 GM terminal test kit, measure the resistance between the speed sensor terminals. Is the speed sensor resistance within the specified value?	2WD: 2,600-3,160 Ω 4WD: 1,420-2,140 Ω	Go to Step 5	Go to Step 6
5	Test the output speed sensor circuit between the TCM and output speed sensor for an open or short to ground condition. Refer to Circuit Testing . Did you find and correct the condition?	-	Go to Step 7	-
6	IMPORTANT: Do not rotate the speed sensor in the retaining bracket. Orientation is fixed, and if changed, may cause improper operation. Replace the output speed sensor. Refer to Speed Sensor Replacement .Did you complete the replacement?	-	Go to Step 7	-
7	Perform the following procedure in order to verify the repair: Clear the DTC. Using the scan tool, monitor the output speed sensor operation. Select Specific DTC. Enter DTC P0721. Has the test run and passed?	-	Go to Step 8	Go to Step 2
8	With the scan tool, observe the stored information, capture info and DTC info. Does the scan tool display any DTCs that you have not diagnosed?	-	Go to Diagnostic Trouble Code (DTC) List - Vehicle	System OK