Test Description

WARNING: This page is about a different car, the 2005 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.

The number below refers to the step number on the diagnostic table.

3: This step tests the integrity of the engine harness and TCM by checking for the Signal C state change from HI to LOW. A LOW signal indicates the fault is in the internal transmission harness or the switch. A HI signal indicates the fault is in the engine harness or the TCM.

DTC P1826

Step	Action	Value(s)	Yes	No
1	Did you perform the Diagnostic System Check - Vehicle?	-	Go to Step 2	Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2	Install a scan tool. Turn ON the ignition with the engine OFF. IMPORTANT: Before clearing the DTC, use the scan tool in order to record the ECM Freeze Frame and the TCM Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the ECM and the TCM. Using the Clear Info function erases stored DTCs in both the ECM and TCM. Record the DTC Freeze Frame and Failure Records. Clear the DTC. Select Transmission Data on the scan tool. Select IMS range on the scan tool. Place the range selector in D. Does the scan tool IMS range indicate Drive?	-	Go to Intermittent Conditions in Engine Controls - 3.6L or Intermittent Conditions in Engine Controls - 4.6L	Go to Step 3
3	Turn OFF the ignition. Disconnect the AT inline 20-way connector. Additional DTCs may set. Install the J 45681 jumper harness on the TCM side of the AT inline 20-way connector. See Special Tools . Using the J 35616 GM terminal test kit, connect a fused jumper wire from the TR signal C circuit of the J 45681 to ground. See Special Tools . Refer to Automatic Transmission Inline 20-Way Connector End View (5L40-E) or Automatic Transmission Inline 20-Way Connector End View (5L50-E) . Turn ON the ignition, with the engine OFF. Select IMS A/B/C/P on the scan tool. Does IMS Signal C indicate LOW?	-	Go to Step 5	Go to Step 4
4	Test the TR signal C circuit of the transmission manual shift shaft switch assembly for an open between the TCM connector and the AT inline 20-way connector. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct a condition?	-	Go to Step 9	Go to Step 8
5	Test the TR signal C circuit of the transmission manual shift shaft switch assembly for an open between the AT inline 20-way connector and the switch. Refer to Testing for Continuity in Wiring Systems. Did you find the condition?	-	Go to Step 6	Go to Step 7
6	Replace the automatic transmission wiring harness. Refer to Transmission Internal Electrical Harness Replacement . Is the action complete?	-	Go to Step 9	-
7	Replace the transmission manual shift shaft switch assembly. Refer to Manual Shaft Shift Position Switch Replacement . Is the action complete?	-	Go to Step 9	-
8	Replace the TCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Is the action complete?	-	Go to Step 9	-
9	Perform the following procedure in order to verify the repair: Select DTC. Select Clear Info. Start and idle the engine in PARK. Observe IMS A/B/C/P on the scan tool. Move the range selector to D2, D3, D4 and D positions. Ensure that IMS Signal C indicates LOW for each range. Operate the vehicle to greater than 8 km/h (10 mph) in all gears. Select Specific DTC. Enter DTC P1826. Has the test run and passed?	-	Go to Step 10	Go to Step 2
10	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 in Vehicle DTC Information	System OK