GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2005 🢒 Ascender - 4WD 🢒 DTC 🢒 DTC P1634

Circuit Description

The powertrain control module (PCM) receives the following ignition inputs from the ignition switch:

    • The ignition 0 signal
    • The ignition 1 signal
    • The crank signal

The PCM uses a class 2 Ignition mode message and the voltage input from 2 separate systems to test the ignition 1 circuit. If the PCM detects an improper ignition 1 signal, DTC P1634 will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1634 Ignition 1 Switch Circuit

Conditions for Running the DTC

There is no class 2 serial data circuit condition.

Conditions for Setting the DTC

The ignition 1 signal is present, but the ignition 0 signal is not.

Action Taken When the DTC Sets
    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • The driver information center, if equipped, may display a message.

Conditions for Clearing the DTC
    • A current DTC Last Test Failed clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
    • Clear the DTC with a scan tool.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Does the engine run with the ignition OFF?

Go to Step 6

Go to Step 3

3

Are DTCs P0740, P0753, P0785, or P1860 also set?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Disconnect the powertrain control module (PCM).
  3. Connect a test lamp between the ignition 1 voltage circuit and a good ground.
  4. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

Go to Step 7

Go to Step 5

5

Test the ignition 1 voltage circuit for an open between the splice and the PCM. Refer to Testing for Continuity and Circuit Testing in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

--

6
  1. Disconnect the PCM.
  2. Test both ignition 1 voltage circuits for a short to voltage. Refer to Testing for a Short to Voltage and Circuit Testing in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

--

7

Test for an intermittent and for poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Circuit Testing in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Go to Step 8

8

Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 9

--

9
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 10

10

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK