• | 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. |
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 | -- |
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 |
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 .
• | 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. |
• | 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. |
• | The engine speed is greater than 560 RPM for 5 seconds. |
• | A CRANK request signal has been requested for 409 seconds or greater. |
The IMS signal A is continuously low this ignition cycle, and the IMS indicates transitional position D4-D3 for 8 seconds or greater.
The IMS signal B is continuously high this ignition cycle, and the IMS indicates transitional position D2-D1 for 8 seconds or greater.
The IMS signal P is continuously low this ignition cycle, and the IMS indicates transitional position N-D4 for 8 seconds or greater.
The TCM detects an invalid combination of IMS signals for 8 seconds or greater.
The TCM detects IMS signal C is high, while the gear radio indicates first, second, third, or fourth gear for 8 seconds or greater.
The IMS does not indicate PARK or NEUTRAL for 2 seconds or greater when attempting to start the vehicle.
• | 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. |
DTC P1820, P1822, P1823, P1825, P1826, and P1915 are type B DTCs.
Automatic Transmission Controls Schematics
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Control Module References for scan tool information
• | J 35616 GM Terminal Test Kit |
• | J 44152 Jumper Harness (20 pins) |
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.
⇒ | 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. |
⇒ | 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. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for TCM replacement, setup, and programming.