Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC P1820: Internal Mode Switch A Circuit Low VoltageDTC 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
Circuits | Short to Ground | Open/High Resistance | Short to Voltage |
|---|---|---|---|
TR Signal A | P1820, P1825, P1915 | P1825, P1915 | -- |
TR Signal B | P1825, P1915 | P1822, P1825, P1915 | -- |
TR Signal C | P1825, P1915 | P1826, P1825, P1915 | -- |
TR Signal P | P1823, P1825, P1915 | P1825, P1915 | -- |
Typical Scan Tool Data
Gear Selector Position | A | B | C | P | ||||
|---|---|---|---|---|---|---|---|---|
Park | LOW | HI | HI | LOW | ||||
Park/Reverse | LOW | LOW | HI | LOW | ||||
Reverse | LOW | LOW | HI | HI | ||||
Reverse/Neutral | HI | LOW | HI | HI | ||||
Neutral | HI | LOW | HI | LOW | ||||
Neutral/Drive 4 | HI | LOW | LOW | LOW | ||||
Drive 4 | HI | LOW | LOW | HI | ||||
Drive 4/Drive 3 | LOW | LOW | LOW | HI | ||||
Drive 3 | LOW | LOW | LOW | LOW | ||||
Drive 3/Drive 2 | LOW | HI | LOW | LOW | ||||
Drive 2 | LOW | HI | LOW | HI | ||||
Drive 2/Drive 1 | HI | HI | LOW | HI | ||||
Drive 1 | HI | HI | LOW | LOW | ||||
Invalid | HI | HI | HI | HI | ||||
LOW | HI | HI | HI | |||||
HI | HI | HI | LOW | |||||
| ||||||||
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 .
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
Connector End View Reference
Description and operation
Transmission General Description
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
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
- Ignition OFF, disconnect the transmission 20-way harness connector.
- 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.
- Ignition ON, verify that the affected IMS A/B/C/P parameter is HI.
- 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.
- If all circuits test normal, test or replace the internal transmission wiring harness or the internal mode switch.
| ⇒ | If greater than the specified range test the low reference circuit for an open/high resistance. |
| ⇒ | 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. |
| • | 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. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
| • | Control Module References for TCM replacement, setup, and programming |
