GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Seville - RHD 🢒 DTC 🢒 DTC P1635

Circuit Description

The powertrain control module (PCM) uses the 5-volt reference 1 circuit as a sensor feed to the following sensors:

    • The throttle position (TP) sensor
    • The manifold absolute pressure (MAP) sensor
    • The exhaust gas recirculation (EGR) valve pintle position sensor

The PCM monitors the voltage on the 5-volt reference 1 circuit. If the voltage is out of tolerance, the PCM will set DTC P1635.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC
    • The PCM detects a voltage out of tolerance condition on the 5-volt reference 1 circuit.
    • The above condition is present for longer than 10 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • 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 emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

DTC P1635 - 5 Volt Reference 1 Circuit

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

--

Go to Step 3

Go to Intermittent Conditions

3
  1. Visually and physically inspect the PCM and engine grounds. Ensure that the grounds are clean and secure.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 13

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Disconnect the EGR valve electrical connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Using a DMM, measure voltage between the 5-volt reference circuit and engine ground.

Is voltage near the specified value indicated?

5 V

Go to Step 6

Go to Step 5

5

Is voltage more than the specified value?

5 V

Go to Step 9

Go to Step 7

6
  1. Reconnect EGR Valve.
  2. Disconnect throttle position sensor.
  3. Using a DMM, measure voltage between the 5-volt reference 1 circuit and engine ground.

Is voltage near the specified value indicated?

5 V

Go to Intermittent Conditions

Go to Step 10

7
  1. Monitor DMM while disconnecting all other devices connected to the 5-volt reference circuit one at a time.
  2. If voltage changes when one of the above components are disconnected, replace the component. Refer to appropriate replacement procedure.

Was a component replaced?

--

Go to Step 13

Go to Step 8

8
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Check the 5-volt reference circuit for a short to ground or any sensor low reference circuit.
  4. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 13

Go to Step 12

9
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Turn ON the ignition, with the engine OFF.
  4. Check the following circuits for a short to voltage:
    5. • The 5-volt reference circuit.
    • The manifold absolute pressure MAP sensor signal circuit.
  5. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 13

Go to Step 12

10

Check for a short between the EGR control high circuit and the 5-volt reference circuit and repair as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 13

Go to Step 11

11

Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .

Is the action complete?

--

Go to Step 13

--

12

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 13

--

13
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 14

Go to Step 2

14

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK