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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2000 🢒 Impala 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P1635 5 Volt Reference Circuit

Refer to Engine Controls Schematics

Fuel Controls


Object Number: 488641 Size: FS
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
FOG RLY, F/PMP RLY, DLR/EXT LTS, EXT LTS, A/C RLY (CMPR), PCM and HORN RLY Fuses
G302
G203 (3 of 3)
G203 (2 of 3)
Handling ESD Sensitive Parts Notice
Engine Controls Components
Powertrain Control Module Description
Fuel Injectors
Ignition System, Knock Sensors
OBD II Symbol Description Notice
 ,

Engine Data Sensors: A/C Pressure Refrig, TP, MAP, ECT, IAT
Object Number: 489428 Size: FS
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Engine Controls Components
Powertrain Control Module Description
Engine Data Sensors - HO2S 1, HO2S 2
Fuel Injectors
OBD II Symbol Description Notice
 and

IAC, Engine Oil Level, Engine Oil Pressure, EGR, EVAP Vent
Object Number: 489429 Size: FS
ABS/PCM, STOP, TURN SIGNAL and SRS Fuses
G113 - Continued
Engine Controls Components
Powertrain Control Module Description
VSS, Cruise
Engine Data Sensors - MAF, EVAP Purge, Air Injection
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
 .

Circuit Description

The PCM uses the 5 volt reference A circuit as a sensor feed to the following sensors:

    • The TP sensor
    • The MAP sensor
    • The EGR Valve pintle position sensor
    • Fuel tank pressure sensor

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

Conditions for Setting the DTC
    • The PCM detects voltage out of tolerance 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 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

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

Check for the following conditions:

    • Poor connection at the PCM -- Inspect harness connectors for the following conditions:
       - Backed out terminals
       -  Improper mating
       - Broken locks
       -  Improperly formed or damaged terminals
       -  Poor terminal to wire connection
    • Damaged harness -- Inspect the wiring harness for damage. If the harness appears to be OK, observe the MAP display on the scan tool turn ON the ignition, with the engine OFF while moving connectors and wiring harnesses related to the following sensors. A change in the MAP display will indicate the location of the malfunction.
       - The TP sensor
       - The FTP sensor
       - The EGR valve
       - The MAP sensor

If the DTC cannot be duplicated and is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set. Also refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

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. Refer to PCM Replacement/Programming .

DTC P1635 - 5 Volt Reference A Circuit

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
  1. Visually and physically check 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.

Did you find a problem?

--

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 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 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 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. Check 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 11

Go to Step 10

8
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Turn ON the ignition.
  4. Check 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 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

Important:: The replacement PCM must be programmed.

Replace PCM. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 11

--

11
  1. Review and record scan tool Failure Records data.
  2. Clear DTCs.
  3. Operate the vehicle within Failure 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