4T80-E - Automatic Transaxle

DTC P1820, P1822, P1823, P1825, P1826, or P1915

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* ReviewStrategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.


DTC Descriptors
DTC P1820
- Internal Mode Switch A Circuit Low Voltage

DTC P1822
- Internal Mode Switch B Circuit High Voltage

DTC P1823
- Internal Mode Switch P Circuit Low Voltage

DTC P1825
- Internal Mode Switch - Invalid Range

DTC P1826
- Internal Mode Switch C Circuit High Voltage

DTC P1915
- Internal Mode Switch Does Not Indicate Park/Neutral (P/N) During Start



Diagnostic Fault Information





Typical Scan Tool Data





Circuit/System Description

The internal module switch (IMS) is a sliding contact switch attached to the selector detent inside the transmission side cover. The 4 inputs to the transmission control module (TCM) indicate the transmission range selector position. The input voltage level at the TCM is high, B+, when the IMS is open and low, 0 volts, when the switch is closed. The 4 input parameters represented are Signals A, B, C and P. Refer to Transmission Internal Mode Switch Logic (Transmission Internal Mode Switch Logic).

Conditions for Running the DTC

P1820, P1822 or P1823
* The ignition voltage is between 8 and 18 volts.
* The engine speed is between 500 and 6,500 RPMs for 5 seconds.
* The IMS indicates PARK for at least 1 second.
* No engine torque malfunction.
* The engine torque is between 50-1,492 N.m (37-1,100 lb ft).


P1825
* The ignition voltage is between 8 and 18 volts.
* The engine speed is between 500 and 6,500 RPMs for 5 seconds.


P1826
* DTCs P0722 or P0723 are not set.
* The ignition voltage is between 8 and 18 volts.
* The engine torque is between 50-1,492 N.m (37-1,100 lb ft).
* The vehicle speed is at least 16 km/h (10 mph).
* The gear ratio is between 2.75 and 3.16 OR
* The gear ratio is between 1.51 and 1.74 OR
* The gear ratio is between 0.93 and 1.06 OR
* The gear ratio is between 0.63 and 0.72


P1915
* The ignition voltage is between 8 and 18 volts.
* The engine speed is between 500 and 6,500 RPMs for 5 seconds.
* The engine is cranking for more than 2.5 seconds.


Conditions for Setting the DTC

P1820

The IMS A signal is low for more than 4 seconds when the vehicle is in DRIVE.

P1822

The IMS B signal is high for more than 4 seconds when the vehicle is in DRIVE.

P1823

The IMS P signal is low for more than 4 seconds when the vehicle is in DRIVE.

P1825

The IMS signal is invalid for more than 4 seconds.

P1826

The IMS C signal is high for more than 4 seconds when the vehicle is in DRIVE.

P1915

The IMS signal does not indicate PARK or NEUTRAL for more than 1 second when the engine is cranking.

Action Taken When the DTC Sets

DTCs P1820, P1822, P1823, P1825, P1826, and P1915 are Type B DTCs.

Conditions for Clearing the DTC

DTCs P1820, P1822, P1823, P1825, P1826, and P1915 are Type B DTCs.

Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and operation

Transmission General Description (Transmission General Description)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference

Control Module References (Programming and Relearning)
Special Tools

* J 35616 GM-Approved Terminal Test Kit
* J 44152 Jumper Harness (20 pins)


Circuit/System Verification

Ignition ON, use a scan tool to verify the IMS A/B/C/P parameter matches the typical scan tool data table as the transmission shift lever is moved through the ranges from PARK to L1.

Circuit/System Testing

1. Ignition OFF, disconnect the transmission 20-way harness connector.
2. Ignition OFF, test the TCM side of the transmission 20-way harness connector for less than 5 ohms of resistance between the low reference circuit terminal K and ground.

• If greater than the specified range test the low reference circuit for an open/high resistance.

3. Ignition ON, verify that the affected IMS A/B/C/P parameter is HI.

• If LOW test the TCM side of the 20-way harness connector signal circuit for a short to ground. If the circuit tests normal, replace the TCM.

4. Install a 3-amp fused jumper wire between the signal circuit and the low reference circuit on the TCM side of the transmission 20-way harness connector. Verify the affected IMS A/B/C/P parameter is LOW.

* Terminals F and K for IMS A.
* Terminals G and K for IMS B.
* Terminals H and K for IMS C.
* Terminals J and K for IMS P.

• If HI test the signal circuit of the affected IMS for a short to voltage or an open/high resistance. If the circuit tests normal, replace the TCM.

5. If all circuits test normal, test or replace the internal transmission wiring harness or the internal mode switch.


Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.

* Lower Control Valve Body and Internal Mode Switch Installation (Overhaul)
* Control Module References (Programming and Relearning) for TCM replacement, setup, and programming