Circuit Description
The transmission internal mode switch (IMS) is a sliding contact switch attached to the selector detent inside the transmission side cover. The four inputs to the PCM indicate the position of the transmission range selector. The input voltage level at the PCM is high (B+) when the IMS is open and low when the switch is closed to ground. The four input parameters represented are Signals A, B, C and P (Parity). Refer to Transmission Internal Mode Switch Logic .
If the PCM detects that IMS Signal C is high while being driven in a forward range, then DTC P1826 sets. DTC P1826 is a type C DTC.
Conditions for Running the DTC
| • | The system voltage is 9-18 volts. |
| • | The engine speed is at least 500 RPM for 5 seconds and not in fuel shutoff. |
| • | No VSS DTCs P0502 or P0503. |
| • | Vehicle speed is greater than 14 km/h (10 mph). |
| • | The engine torque is greater than 27 N·m (20 lb ft). |
| • | DTC P1826 has not passed this key cycle. |
Conditions for Setting the DTC
The PCM detects IMS Signal C is high, while the gear ratio indicates first, second or third gear for 0.5 seconds.
Action Taken When the DTC Sets
| • | The PCM does not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Failure Records. |
| • | The PCM stores DTC P1826 in PCM history. |
Conditions for Clearing the DTC
| • | A scan tool can clear the DTC. |
| • | The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without a non-emission-related diagnostic fault occurring. |
| • | The PCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the PCM. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls in Engine Controls |
2 |
Important: Before clearing the DTC, use the Scan Tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM. Does the Scan Tool IMS parameter indicate Drive 4? | -- | Go to Intermittent Conditions in Engine Controls | Go to Step 3 |
Refer to Automatic Transmission Inline Harness Connector End View . Does IMS signal C indicate LOW? | -- | Go to Step 5 | Go to Step 4 | |
4 | Test the signal C circuit (CKT 773) of the IMS for an open between the PCM connector C1 and the AT Inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct a condition? | -- | Go to Step 9 | Go to Step 8 |
5 |
Refer to Circuit Testing 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 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 Transmission Overhaul in the 4T65-E Section of the Transmission Unit Repair Manual. Did you complete the replacement? | -- | Go to Step 9 | -- |
8 | Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls. Did you complete the replacement? | -- | Go to Step 9 | -- |
9 | Perform the following procedure in order to verify the repair:
Ensure that IMS signal C indicates LOW for each drive range. Has the test run and passed? | -- | System OK | Go to Step 1 |
