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For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 1999 🢒 Intrigue 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P1635 5 Volt Reference Circuit

Object Number: 154590 Size: LF
Engine Controls Components
Engine Data Sensors
OBD II Symbol Description Notice

Circuit Description

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

    • The throttle position (TP) sensor.
    • The manifold absolute pressure (MAP) sensor.
    • The EGR valve pintle position sensor.

The PCM monitors the voltage on the 5 volt Reference A circuit. If the voltage is out of tolerance, the PCM sets DTC P1635.

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 PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has run and failed.
    • The PCM stores the conditions which were present when the DTC set as Freeze Frame and Fail Records data.

Conditions for Clearing the MIL/DTC
    • The PCM turns the MIL off during the third consecutive trip in which the diagnostic has run and passed.
    • The history DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.
    • The DTC may be cleared using the scan tool Clear Info function or by disconnecting the PCM battery feed.

Diagnostic Aids

Important:: Verify that the PCM and engine grounds are secure and clean.

Inspect for the following conditions:

    • A faulty connection at the PCM. Inspect the harness and the connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connections.
    • 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 with the engine not running while moving the connectors and the wiring harnesses related to the following sensors. A change in the MAP display indicates the location of the malfunction.
       - The TP sensor.
       - The MAP sensor.
       - The EGR valve.

Reviewing the Fail 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(s) below refer to the step number(s) on the Diagnostic Table.

  1. A malfunctioning EGR valve can leak a small amount of current from the ignition feed circuit to the 5 volt reference A circuit. If the problem does not exist with the EGR valve disconnected, replace the EGR valve.

    2.

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

DTC P1635 - 5 Volt Reference A Circuit

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Visually/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  14

Go to Step 3

3

Use a scan tool in order to select DTC info, Last Tst Fail and record any other DTCs set.

Are any other DTCs set?

--

Go to applicable DTCs first.

Go to Step 4

4
  1. Turn off the ignition switch.
  2. Disconnect the PCM.
  3. Turn on the ignition switch.
  4. Use a digital multimeter (DMM) in order to measure the voltage between the 5 volt reference A circuit and the PCM ground circuit at the PCM harness connector.

Is voltage more than the specified value?

5.5 V

Go to Step 5

Go to Step 9

5

Monitor the DMM connected between the 5 volt reference A circuit and the PCM ground circuit while disconnecting the EGR valve.

Is the voltage more than the specified value with the EGR valve disconnected?

5.5 V

Go to Step 6

Go to Step  8

6
  1. Monitor the DMM connected between the 5 volt reference A circuit and the PCM ground circuit while disconnecting the following sensors one at a time:
    2. • The throttle position (TP) sensor
    • The manifold absolute pressure (MAP) sensor
    • The engine oil pressure sensor
  2. If voltage changes when one of the above components is disconnected, locate and repair a short to voltage in the affected sensor signal circuit. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step  14

Go to Step 7

7
  1. Turn off the ignition switch.
  2. Disconnect the PCM.
  3. Turn on the ignition switch.
  4. Test the 5 volt reference A circuit for a short to voltage.
  5. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step  14

Go to Step 13

8

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

Did you complete the repair?

--

Go to Step  14

--

9
  1. Turn off the ignition switch.
  2. Reconnect the PCM.
  3. Disconnect the following components:
    4. • The TP sensor.
    • The MAP sensor.
    • The EGR valve.
    • The engine oil pressure sensor.
  4. Turn on the ignition switch.
  5. Connect the DMM in order to measure voltage between the 5 volt reference A circuit and the sensor ground circuit at the TP sensor harness connector.

Is the voltage less than the specified value?

4.5 V

Go to Step 12

Go to Step 10

10
  1. Monitor the DMM connected between the 5 volt reference A circuit and the sensor ground circuit while reconnecting the following components one at a time:
    2. • The MAP sensor.
    • The EGR valve.
  2. If the voltage changes when one of the above components is reconnected, replace the affected component.

    3. Refer to Manifold Absolute Pressure Sensor Replacement .

Was a problem found?

--

Go to Step  14

Go to Step 11

11
  1. Disconnect the EGR valve.
  2. Connect the DMM in order to measure voltage between the 5 volt reference A circuit and the sensor ground circuit at the EGR valve harness connector
  3. Monitor the voltage while reconnecting the TP sensor.
  4. If the voltage changes when the TP sensor is reconnected, replace the TP sensor. Refer to Throttle Position Sensor Replacement .

Was a problem found?

--

Go to Step  14

Go to Step 13

12
  1. Turn off the ignition switch.
  2. Disconnect the PCM.
  3. Test the 5 volt reference A circuit for a short to ground.
  4. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step  14

Go to Step 13

13

Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Replace PCM.

Did you complete the repair?

--

Go to Step  14

--

14
  1. Review and record the scan tool Fail Records data.
  2. Clear any DTCs.
  3. Operate the vehicle within the Fail Records conditions.
  4. Use the scan tool in order to monitor the Specific DTC info for DTC P1635 until the DTC P1635 test runs.

Does the scan tool indicate DTC P1635 Failed This Ign?

--

Go to Step 2

System OK