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Test Description

WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 3:  A low value for Signal A indicates a short to ground in the engine harness or the TCM.
  2. 5:  This step tests the internal transmission harness. A value of LOW for Signal A indicates the fault is in the harness. Otherwise the fault will be in the switch.
DTC P1820 (3.6L)

Step Action Value(s) Yes No
1 Did you perform the Diagnostic System Check - Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls in Engine Controls - 3.6L
2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
    3. IMPORTANT: Before clearing the DTC, use the scan tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the TCM.
  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. Select IMS on the scan tool.
  6. Place the range selector in D4.
Does the scan tool IMS parameter indicate Drive 4?		 - Go to Intermittent Conditions in Engine Controls - 3.6L Go to Step 3 
3 
  1. Turn OFF the ignition.
  2. Disconnect the AT Inline 20-way connector. Additional DTCs may set.
  3. Turn ON the ignition, with the engine OFF.
  4. Select IMS A/B/C/P on the scan tool.
Does IMS signal A indicate LOW?		 - Go to Step 4  Go to Step 5 
4 Test the TR signal A circuit of the IMS for a short to ground between the TCM connector and the AT Inline 20-way connector.
Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 9  Go to Step 8 
5 
  1. Turn OFF the ignition.
  2. Reconnect the AT Inline 20-way connector.
  3. Disconnect the automatic transmission wiring harness at the IMS.
  4. Turn ON the ignition, with the engine OFF.
  5. Select IMS A/B/C/P on the scan tool.
Does IMS signal A indicate LOW?		 - Go to Step 6  Go to Step 7 
6 Replace the automatic transmission wiring harness.
Refer to Wiring Harness Replacement .
Did you complete the replacement?		 - Go to Step 9  -
7 Replace the lever assembly-manual shaft detent with internal mode switch.
Refer to Manual Shift Shaft Position (Internal Mode) Switch and Parking System Components Removal in Transmission Unit Repair article.
Did you complete the replacement?		 - Go to Step 9  -
8 Replace the TCM.
Refer to Module, Transmission Control - Replace .
Did you complete the replacement?		 - Go to Step 9  -
9 Perform the following procedure in order to verify the repair:
  1. Select DTC.
  2. Select Clear Info.
  3. Start and idle the engine in PARK for 10 seconds.
  4. Select IMS A/B/C/P on the scan tool.
  5. Move the range selector from PARK to D4.
  6. Ensure that IMS signal A changes from LOW to HI.
  7. Select Specific DTC.
  8. Enter DTC P1820.

Has the test run and passed?		 - Go to Step 10  Go to Step 2 
10 With a 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 in Engine Controls - 3.6L System OK
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