P1825

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 from the IMS indicate which position is selected by the transmission selector lever. This information is used for engine controls as well as determining the transmission shift patterns. 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 state of each input is available for display on the scan tool. The four input parameters displayed are Input A, Input B, Input C and Input P (Parity).

If the PCM detects an invalid transmission range for 5 seconds with the engine running, then DTC P1825 sets. DTC P1825 is a Type D DTC.

Conditions for Running the DTC

^ The system voltage is 918 volts.

^ The engine speed is at least 500 RPM for 5 seconds and not in fuel shutoff.

Conditions for Setting the DTC

The PCM detects an invalid combination of MS signals for 5 seconds.

Action Taken When the DTC Sets

^ The PCM does not illuminate the malfunction indicator lamp (MIL).

^ The PCM stores DTC P1825 in PCM history.

Conditions for Clearing the DTC

^ A scan tool clears the DTC from the PCM history.

^ The PCM clears the DTC from the PCM history if the vehicle completes 40 consecutive warm-up cycles without an emission related diagnostic fault occurring.

^ The PCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids

^ Inspect the wiring for faulty electrical connections at the PCM, the transmission 20-way connector, the IMS connector and all other circuit connecting points for the following conditions:

- A backed out terminal

- A damaged terminal

- Reduced terminal tension

- A chafed wire

- A broken wire inside the insulation

- Moisture intrusion

- Corrosion

^ When diagnosing for an intermittent short or open massage the wiring harness while watching the test equipment for a change.

Test Description

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

3. This step tests for a loose connection or connector related condition.

4. This step tests the PCMs ability to detect a state change on each input circuit.

5. This step tests the input circuits to the PCM on the engine side of the wiring harness.

7. This step tests the input circuits on the transmission side of the wiring harness.

10. Because of harsh conditions inside the transmission repairing the automatic transmission (AT) wiring harness assembly is not acceptable. It must be replaced if it is damaged in any way.