P1820
DTC P1820 (3.8L)
Circuit Description
The transmission internal mode switch (IMS) is a sliding contact switch attached to the selector detent inside the transmission side cover. The 4 inputs to the powertrain control module (PCM) indicate the transmission range selector position. 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 4 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 A is always low, then DTC P1820 sets. DTC P1820 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1820 Internal Mode Switch A Circuit Low Voltage
Conditions for Running the DTC
* No MAP DTC P0107 or P0108.
* The engine torque is 55-407 N.m (40-300 lb ft).
* The engine is running for greater than 5 seconds and not in fuel cut-off.
* The IMS indicates PARK for 2 seconds.
Conditions for Setting the DTC
The IMS Signal A is continuously low this ignition cycle, and the IMS indicates transitional position D4-D3 for 8 seconds.
Action Taken When the DTC Sets
* The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
* The PCM commands maximum line pressure.
* The PCM freezes transmission adaptive functions.
* The PCM assumes D4 for shifting.
* The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
* The PCM stores DTC P1820 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.
Conditions for Clearing the MIL/DTC
* The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
* A scan tool can clear the MIL/DTC.
* The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an 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.
3. A low value for Signal A indicates a short to ground in the engine harness or the PCM.
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 is in the switch.
