For 1990-2009 cars
Engine Controls Components
Engine Data Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts 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 exhaust gas recirculation (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 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 more than 10 seconds.

### Action Taken When the DTC Sets

• | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

• | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.

• | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using a scan tool.

### Diagnostic Aids

Inspect for the following conditions:

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

• | Loose terminal connection

- | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

- | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

• | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

• | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

### Test Description

The numbers below refer to the step numbers on the diagnostic table:

1. This step ensures that the replacement PCM, which utilizes an electrically erasable programmable read only memory (EEPROM), is programmed when installed.

Step | Action | Values | 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 | Visually and physically inspect the PCM and engine grounds. Ensure that the grounds are clean and secure. Refer to Wiring Repairs in Wiring Systems . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 3
3 |

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

Is voltage near the specified value indicated?

5.0 V

Go to Step 5

Go to Step 4

4 | Is voltage less than the specified value indicated? | 4.9 V | Go to Step 6 | Go to Step 8
5 |

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

Is voltage near the specified value indicated?

5.0 V

Go to Step 10

Go to Step 9

6 |

1. Monitor the DMM while disconnecting all other devices connected to 5 volt reference A one at a time.
2. If voltage changes when one of the above components is 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. Test all 5 volt reference A circuits for a short to ground. Refer to Wiring Repairs in Wiring Systems .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

8 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Turn ON the ignition.
4. Test all 5 volt reference A circuits for a short to voltage. Refer to Wiring Repairs in Wiring Systems .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

9 | Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement . Did you complete the replacement? | -- | Go to Step 11 | --
10 | Important: The replacement PCM must be programmed. Replace PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | Go to Step 11 | --
11 |

1. Review and record scan tool Fail Records data.
2. Clear the DTCs.
3. Operate the vehicle within Fail Records conditions.
4. Monitor Specific DTC info for DTC P1635 until the DTC P1635 test runs, using a scan tool.

Does the scan tool indicate DTC P1635 failed this ignition?

--

Go to Step 2

System OK