We have a car that gave us a code P1635. There are other codes, but from what I can gather, they are caused by this code. It is a problem with the 5 volt reference. I did a search and found others with the similar problems. We checked the car out, but haven't found anything obvious. If anyone has a place to look first, I'd appreciate it.
Thanks,
Todd

 

The schematics show 4 sensors connected to that reference. The MAP, Fuel Tank Pressure, A/C Pressure and Oil Pressure Sensors. Did you disconnect each one separately and measure the +5 Volt reference at each? Did you do a continuity check on the reference circuitry to see if there are any opens or a short to battery voltage or ground?

Bill

 

Document ID# 672136
2001 Chevrolet/Geo Corvette


--------------------------------------------------------------------------------

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 manifold absolute pressure (MAP) 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 engine is running.

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

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
Observe the Freeze Frame and/or Failure Records data for this DTC.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame and/or Failure Records data that you observed.
Does the DTC fail this ignition?
--
Go to Step 3
Go to Intermittent Conditions

3
Inspect the PCM and engine grounds. Ensure that the grounds are clean and secure.
If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Was a problem found?
--
Go to Step 12
Go to Step 4

4
Turn OFF the ignition.
Disconnect the MAP sensor electrical connector.
Turn ON the ignition, with the engine OFF.
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
Reconnect MAP sensor.
Disconnect engine oil pressure sensor.
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 Intermittent Conditions
Go to Step 10

7
Monitor DMM while disconnecting the engine oil pressure sensor.
If voltage changes when the sensor is disconnected, replace the component. Refer to Engine Oil Pressure Sensor or Switch Replacement in Instrument Panel Gauges and Console.
Was a component replaced?
--
Go to Step 12
Go to Step 8

8
Turn OFF the ignition.
Disconnect the PCM.
Check the 5-volt reference circuit for a short to ground or any sensor low reference circuit.
If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Was a problem found?
--
Go to Step 12
Go to Step 11

9
Turn OFF the ignition.
Disconnect the PCM.
Turn ON the ignition, with the engine OFF.
Check the following circuits for a short to voltage:
The 5 volt reference circuit.
The manifold absolute pressure MAP sensor signal circuit.
If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Was a problem found?
--
Go to Step 12
Go to Step 11

10
Replace the MAP sensor. Refer to Manifold Absolute Pressure (MAP) Sensor Replacement .

Is the action complete?
--
Go to Step 12
--

11
Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .

Did you complete the replacement?
--
Go to Step 12
--

12
Use the scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
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 13
Go to Step 2

13
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



--------------------------------------------------------------------------------
Document ID# 672136
2001 Chevrolet/Geo Corvette

 

^^ Man your good

 

Todd:
Did you ever find it? Mine is now doing it and shuts down showing low oil pressure.

THanks.

 

Never did find out what was wrong with it. We just cleared the codes and it never has come back.