GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Epica 🢒 Transmission/Transaxle 🢒 Automatic Transmission - ZF 4HP 16 🢒 DTC P1671

Circuit Description

The transmission control module (TCM) is an electronic device which monitors inputs to control various transmission functions including shift quality and transmission sensors, switches, and components to process for use within its control program. Based on this input information, the TCM controls various transmission output functions and devices.

The following information is transmitted between the TCM and the engine control module (ECM) through the controller area network (CAN):

    • Engine malfunction signal
    • Engine speed
    • Engine output torque reduction signal
    • Engine coolant temperature (ECT)

Conditions for Setting the DTC
    • The system voltage is too high or too low.
    • The CAN transmitting wiring harness is shorted or open.
    • The TCM or ECM is defective.

Action Taken When the DTC Sets
    • The malfunction indicator lamp (MIL) will illuminate.
    • The TCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records buffer.
    • Adopt Emergency/Substitute mode and constant 4th gear.
    • After ignition OFF/ON, 3rd gear by hydraulic control, and the positions P, R, and N are also possible.

Conditions for Clearing the MIL/DTC
    • The MIL will turn OFF when the malfunction has not occurred after 3 ignition cycles.
    • A history DTC will clear after 40 consecutive warm-up cycles without a fault.
    • Clear the DTCs with a scan tool.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Automatic Transmission?

--

Go to Step 2

Go to Diagnostic System Check - Automatic Transmission

2
  1. Turn the ignition OFF.
  2. Disconnect the transmission control module (TCM) wiring connector and engine control module (ECM) wiring connector.
  3. Measure the resistance between terminal A8 of the TCM wiring connector and terminal K14 of the ECM wiring connector.
  4. Measure the resistance between terminal A16 of the TCM wiring connector and terminal K15 of the ECM wiring connector.

Is the resistance within the values shown?

0 ohms

Go to Step 4

Go to Step 3

3

Repair the malfunctioning terminals, as necessary.

Is the action complete?

--

System OK

--

4
  1. Turn ON the ignition, with the engine OFF.
  2. Measure the voltage of terminal A8.
  3. Measure the voltage of terminal A16.

Is the voltage within the specified range?

11-14 V

Go to Step 5

Go to Step 6

5

Repair the short to power on the terminal, as necessary.

Is the action complete?

--

System OK

--

6
  1. Replace the TCM. Refer to Transmission Control Module Replacement .
  2. Turn the ignition OFF.
  3. Turn ON the ignition, with the engine OFF.

Did DTC P1671 set?

--

Go to Step 7

Go to Step 8

7

Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls-2.0L or Engine Control Module Replacement in Engine Controls-2.5L.

Is the action complete?

--

Go to Step 8

--

8
  1. After the repair, use a scan tool clear info function and road test the vehicle.
  2. Review the DTC info.

Did the last test fail or is the current DTC displayed?

--

Go to Step 2

System OK