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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2002 🢒 LeSabre 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P1635

Circuit Description

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

    • The fuel tank pressure (FTP) sensor
    • The throttle position (TP) sensor
    • The mass absolute pressure (MAP) sensor
    • The exhaust gas recirculation (EGR) valve pintle position sensor
    • The engine oil pressure sensor

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

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC
    • The PCM detects a voltage out of tolerance condition on the 5-volt reference A 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.

Diagnostic Aids

Important:: Be sure to inspect PCM and engine grounds for being secure and clean.

Check for the following conditions:

    • A poor connection at the PCM--Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
    • A damaged harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the MAP display on the scan tool with the ignition ON, engine not running while moving connectors and wiring harnesses related to the following sensors. A change in the MAP display will indicate the location of the malfunction.

Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Test Description

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

  1. This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read only memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

DTC P1635 - 5 Volt Reference A 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. Inspect the PCM and engine grounds. Ensure that the grounds are clean and secure.
  2. If a condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a condition found?

--

Go to Step 11

Go to Step 3

3
  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 the engine ground.

Is voltage near the specified value indicated?

5 V

Go to Step 5

Go to Step 4

4

Is voltage near the specified value indicated?

0 V

Go to Step 6

Go to Step 8

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

Is voltage near the specified value indicated?

5 V

Go to Step 10

Go to Step 9

6
  1. Monitor DMM while disconnecting all other devices connected to 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 11

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Check the 5-volt reference circuit for a short to ground.
  4. If a condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a condition found?

--

Go to Step 11

Go to Step 10

8
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Turn ON the ignition, with the engine OFF.
  4. Check the 5-volt reference circuit for a short to voltage.
  5. If a condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a condition found?

--

Go to Step 11

Go to Step 10

9

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

Is the action complete?

--

Go to Step 11

--

10

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 11

--

11
  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 12

Go to Step 2

12

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