4T80-E Automatic Transaxle
DTC P1826
Circuit Description
The transmission internal mode switch (IMS) is a sliding contact switch attached to the lower control valve body, within the transmission. The manual valve link assembly then connects the IMS to the manual valve. The four inputs to the transmission control module (TCM) from the IMS indicate which position is selected by the transmission selector lever. This information is used for Computers and Control Systems as well as determining the transmission shift patterns. The input voltage level at the TCM is high, ignition voltage, when the IMS is open and low when the switch is closed to ground. The state of each input is available for display on the scan tool. The four input parameters represented are Signal A, Signal B, Signal C and Signal P, Parity.
If the TCM detects an IMS transitional state between D2 and D1 while the vehicle is in motion, then DTC P1826 sets. DTC P1826 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1826 Internal Mode Switch C Circuit High Voltage
Conditions for Running the DTC
* No OSS DTCs P0722 or P0723.
* The ignition voltage is between 8-18 V.
* The engine torque is 50 N.m (37 lb ft) or greater.
* Vehicle speed is greater than 16 km/h (10 mph).
* DTC P1826 did not pass this cycle.
* Gear ratios
* 1st 3.17:1-2.75:1
* 2nd 1.74:1-1.51:1
* 3rd 1.07:1-0.93:1
* 4th 0.73:1-0.63:1
Conditions for Setting the DTC
The IMS indicates DRIVE for 8 seconds.
Action Taken When the DTC Sets
* The TCM requests the engine control module (ECM) to illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
* The TCM commands maximum line pressure.
* The TCM freezes transmission adaptive functions.
* The ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as Freeze Frame and Failure Records and the TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as Failure Records.
* The TCM stores DTC P1826 in TCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.
Conditions for Clearing the MIL/DTC
* The ECM turns OFF the MIL after the third consecutive drive trip in which the TCM does not send a MIL illumination request.
* The TCM clears the DIC message when the condition no longer exists.
* A scan tool can clear the MIL/DTC.
* The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
* The TCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the TCM.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
3. This step determines if the fault is internal or external to the transmission.
4. This step determines if the engine wiring harness circuit is at fault or the TCM.
5. This step determines if the automatic transmission wiring harness is at fault or the IMS.
