P1812

WITH 4L60-E AUTOMATIC TRANSMISSION

DTC P1812 Transmission Fluid Overtemp Diagnostic Chart:

Transmission Range (TR) Pressure Switch Assembly Wiring Assembly:

CIRCUIT DESCRIPTION
The Transmission Fluid Temperature (TFT) sensor is a thermistor within the Transmission Range (TR) pressure switch assembly that controls the signal voltage to the Vehicle Control Module (VCM-A). The VCM-A supplies a 5 volt reference to the sensor on CKT 1227. When the transmission fluid is cold, the sensor resistance is high and the VCM-A will sense high signal voltage. DTC Type (D).
As the transmission fluid temperature warms to normal transmission operating temperature 100°C (212°F), the sensor resistance becomes less and the voltage decreases to 1.5 to 2.0 volts.

DTC P1812 WILL SET WHEN
Signal voltage indicates a transmission fluid temperature greater than 146°C (295°F) for 30 minutes and no DTC P0712 or P0713 set.

ACTION TAKEN (VCM-A will default to)
DTC P1812 will be stored in the VCM-A memory but will not turn "ON" the MIL (Malfunction Indicator Lamp).

DTC P1812 WILL CLEAR DEFAULT ACTION WHEN
The fault condition(s) no longer exist and the ignition is cycled "OFF" for five seconds, then "ON".

DTC P1812 WILL PASS WHEN
- The VCM-A will report a "PASS" when transmission temperature drops below 137°C (268°F).
- All enable criteria are met.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test checks for skewed sensor or shorted circuit.
2. This test simulates a DTC P0713.

DIAGNOSTIC AIDS
Check harness routing for a potential short to ground in CKT 1227.
Scan tool TFT displays should rise steadily to about 100°C (212°F) then stabilize.
Refer to "VCM-A Intermittents.
The temperature to resistance value scale may be used to test the transmission sensor at the various temperature levels to evaluate the possibility of a "skewed" sensor. A "skewed" sensor could result in delayed garage shifts or Torque Converter Clutch (TCC) complaints.
Check transmission fluid. Refer to Fluid Checking Procedure.
Check for possible customer driving habits, trailer towing etc..