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For 1990-2009 cars only
Makes 🢒 Buick 🢒 1996 🢒 Century 🢒 DTC 🢒 DTC P1812 Transmission Fluid Overtemperature

Object Number: 29323 Size: MF
Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

Circuit Description

The Automatic Transmission Fluid Temperature (TFT) sensor is a negative coefficient thermistor. When the transmission fluid is cold, the sensor resistance is high. As the transmission fluid warms, the sensor resistance decreases. The TFT range is -40 to +140°C (-40 to +284°F).

When the PCM detects a high transmission temperature for an extended period of time on the TFT Sensor circuit, then DTC P1812 sets. DTC P1812 is a type D DTC.

Conditions for Setting the DTC
    • No TFT DTCs P0712 or P0713
    • The transmission fluid temperature is hotter than 130°C (266°F) for more than 7 minutes.

Action Taken When the DTC Sets

The PCM does not illuminate the Malfunction Indicator Lamp (MIL).

Conditions for Clearing the DTC

A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.

Diagnostic Aids
    • Inspect the wiring for poor electrical connections at the PCM. Inspect the wiring at the transmission 7-way connector. Look for the following conditions:
       - A bent terminal
       - A backed out terminal
       - A damaged terminal
       - Poor terminal tension
       - A chafed wire
       - A broken wire inside the insulation
    • When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change.
    • Inspect the transmission cooling system for blockage and restrictions.

Test Description

The number below refers to the step numbers on the diagnostic table.

  1. This step inspects all of the components which could cause a P1812 to set.

DTC P1812 Transmission Fluid Over Temperature

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Have you performed the transmission fluid checking procedure?

--

Go to Step 3

Go to Transmission Fluid Check

3
  1. Install the scan tool (tech 1) ®.
  2. With the engine OFF, turn the ignition switch to the RUN position.

    3. Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.

  3. Record the DTC Freeze Frame and Failure Records.

Was the Automatic Transmission Fluid Temperature (TFT) equal to or hotter than the specified value?

130°C (266°F)

Go to Step 4

--

4

Inspect for the following conditions:

    • The engine is overheated.
    • The vehicle is overloaded.
    • The fluid is contaminated with antifreeze.
    • The filter is clogged.
    • The filter is not properly seated.
    • Low line pressure caused by clogged or restricted cooler lines.
    • The radiator is restricted.

Repair the conditions if necessary.

Did you find and correct a problem?

--

Go to Step 5

--

5

In order to verify your repair, perform the following procedure:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle under the following conditions:
    4. • Turn the ignition switch to the RUN position for more than 5 seconds.
    • The TFT is less than 129°C (264°F).
  4. Select Specific DTC. Enter DTC P1812.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1