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 provide 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 | |
HI = Ignition Voltage LOW = 0 Voltage | ||||
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 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 .
Conditions for Running the DTC
P1820, P1822, P1823, P1825
| • | The engine is running for 5 seconds. |
| • | The IMS indicates PARK for 1 second or greater. |
| • | The engine torque is 50 N·m (37 lb ft) or greater. |
| • | No engine torque malfunction. |
P1826
| • | No OSS DTC P0722 or P0723. |
| • | DTC P1826 has not passed this key cycle. |
| • | The engine is running for 5 seconds. |
| • | The IMS indicates PARK for 1 second or greater. |
| • | The engine torque is 50 N·m (37 lb ft) or greater. |
| • | Vehicle speed is 16 km/h (10 mph) or greater. |
| • | No engine torque malfunction. |
P1915
| • | The engine speed is greater than 560 RPM for 5 seconds. |
| • | A CRANK request signal has been requested for 409 seconds or greater. |
Conditions for Setting the DTC
P1820
The IMS signal A is continuously low this ignition cycle, and the IMS indicates transitional position D4-D3 for 8 seconds or greater.
P1822
The IMS signal B is continuously high this ignition cycle, and the IMS indicates transitional position D2-D1 for 8 seconds or greater.
P1823
The IMS signal P is continuously low this ignition cycle, and the IMS indicates transitional position N-D4 for 8 seconds or greater.
P1825
The TCM detects an invalid combination of IMS signals for 8 seconds or greater.
P1826
The TCM detects IMS signal C is high, while the gear radio indicates first, second, third, or fourth gear for 8 seconds or greater.
P1915
The IMS does not indicate PARK or NEUTRAL for 2 seconds or greater when attempting to start the vehicle.
Action Taken When the DTC Sets
| • | DTC P1820, P1822, P1823, P1825, P1826, and P1915 are type B DTCs. |
| • | The TCM commands maximum line pressure. |
| • | The TCM assumes a D4 shift pattern. |
| • | The TCM freezes transmission adaptive functions. |
Conditions for Clearing the DTC
DTC P1820, P1822, P1823, P1825, P1826, and P1915 are type B DTCs.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics
Connector End View Reference
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Special Tools
| • | J 35616 GM Terminal Test Kit |
| • | J 44152 Jumper Harness (20 pins) |
Circuit/System Verification
Start and idle the engine. Using the scan tool, observe the IMS A/B/C/P parameter. The scan tool should display LOW/HI/HI/LOW. Move the gear selector through all ranges and ensure the IMS A/B/C/P parameter matches the gear selector for each selected range.
Circuit/System Testing
- Using the scan tool, does the IMS A/B/C/P parameter display HI/HI/HI/HI for each range selected.
- Turn OFF the ignition. Disconnect the automatic transmission inline 20-way connector. Additional DTCs may set. Turn ON the ignition, with the engine OFF. Observe the IMS A/B/C/P parameter on the scan tool. The parameter should display HI/HI.
- Turn OFF the ignition. Install the J 44152 jumper harness (20 pins) on the engine side of the automatic transmission inline 20-way connector. Turn ON the ignition, with the engine OFF. Using the DMM and the J 35616 GM terminal test kit, measure the voltage at each of the TR signal circuits at the J 44152 .
- Turn OFF the ignition. Install the J 44152 on the transmission side of the automatic transmission inline 20-way connector. Measure the resistance for each TR signal circuit between the J 44152 circuit and the transmission case. The resistance should be greater than 10 ohms.
- Connect the automatic transmission 20-way inline connector. Turn ON the ignition, with the engine OFF. Place the range selector in D3. Observe the IMS A/B/C/P parameter on the scan tool. The IMS A/B/C/P parameter should display LOW/LOW/LOW/LOW.
- If all circuits and connections test normal, test or replace the IMS switch.
| ⇒ | If the IMS A/B/C/P parameter displays HI/HI/HI/HI for each range selected, repair the open in the IMS ground circuit. |
| ⇒ | If the IMS A/B/C/P parameter does not display HI/HI/HI/HI, repair the short to ground in the TR signal circuit that displayed LOW between the TCM and the automatic transmission 20-way inline connector. |
| ⇒ | If the voltage is less than battery voltage, test the affected TR signal for an open between the TCM and the automatic transmission 20-way inline connector. |
| ⇒ | If the resistance is less than 10 ohms, test the affected TR signal for a short to ground between the automatic transmission 20-way inline connector and the IMS switch. |
| ⇒ | If any of the TR signal circuits do not display LOW when the range selector is placed in D3, test the affected TR signal for an open or high resistance between the automatic transmission 20-way inline connector and the IMS switch. |
Component Testing
- Disconnect the automatic transmission inline 20-way connector. Install the J 44152 on the transmission side of the connector and use J 35616 . Referencing Transmission Internal Mode Switch Logic , test for continuity between the IMS ground circuit and each TR signal circuit at the transmission side of the automatic transmission inline 20-way connector, when Transmission Internal Mode Switch Logic indicates the signal circuit should be LOW.
- Measure the resistance between each of the TR signal circuits and the transmission case. The resistance should be greater than 10 ohms.
- If all circuits and connections test normal and the IMS switch tests normal, replace the TCM switch.
| ⇒ | If any TR signal circuits do not display continuity when the table indicates it should be LOW, test the affected TR signal circuit for an open or high resistance between the automatic transmission inline 20-way connector and the IMS switch. |
| ⇒ | If any of the TR signal circuits display less than 10 ohms, test the affected TR signal for a short to ground. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for TCM replacement, setup, and programming.
