Find a good tuner in your area...

Bring the car to them and let them have at it.(tune)

I don't know how far a drive it is but I would suggest AAAndy.

Make the appointment. IMO

 

Team, thanks. On my 03 it was the gas cap. One big turn after resetting the code and it was fixed. This is a very valuable forum. Again, thanks.

 

ok, what is the P1639 code? 5v of what, where, why.
I keep getting this on my newly acquired 97, and I'm lost.
Any help in pointing to the direction of correction, would be greatly appreciated.

 

Sounds like you have a short to ground on the 5 VDC sensor circuit for the following

.The Fuel Tank Pressure sensor
The A/C Refrigerant Pressure sensor
Heres the service manua write up:




DTC P1639 5 Volt Reference 2 Circuit




Circuit Description
The PCM uses a common 5 volt reference 2 circuit as a sensor feed. This circuit supplies 5 volts to the following sensors:

The Fuel Tank Pressure sensor
The A/C Refrigerant Pressure sensor
The PCM monitors the voltage on the 5 volt reference circuit. If the voltage is out of range, this DTC sets.

Conditions for Running the DTC
The engine operating.

Conditions for Setting the DTC
The 5 volt reference circuit is out of range.
The above condition is present for greater than 2 seconds.
Action Taken When the DTC Sets
The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.
Conditions for Clearing the MIL/DTC
The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Use a scan tool in order to clear the MIL and the DTC.
Diagnostic Aids

Important
Remove any debris from the PCM\TAC module connector surfaces before servicing the PCM\TAC module. Inspect the PCM\TAC module connector gaskets when diagnosing/replacing the modules. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM\TAC modules.
For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter Kit J 35616-A . Using this kit prevents damage to the harness/component terminals. Refer to Using Connector Test Adapters in Wiring Systems.

A fuel level sensor (right tank) signal circuit that is shorted to B+ may set this DTC.
For an intermittent condition, refer to Symptoms .
Test Description
The numbers below refer to the step numbers on the diagnostic table.

The 5 volt reference circuits for the sensors are connected together inside the PCM. Both DTCs P1635 and P1639 set at the same time, indicates a 5 volt reference circuit is shorted to a voltage.

The 5 reference circuits for the sensors are connected together inside the PCM. When only P1639 is set, this indicates a short to ground on one of the 5 reference circuits for the A/C Refrigerant Pressure sensor or the Fuel Tank Pressure sensor.

This step determines if a 5 volt reference circuit is shorted to ground.

The 5 volt reference circuits may be shorted to another PCM circuit. The shorted circuit may not be apparent when the PCM harness connector is disconnected. Testing continuity from each 5 volt reference circuit isolates the shorted 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
Install a scan tool.
Start the engine.
Idle the engine for 2 minutes.
Monitor the DTCs using a scan tool.
Did both DTCs P1635 and P1639 fail this ignition?
--
Go to DTC P1635 5 Volt Reference 1 Circuit
Go to Step 3

3
Did DTC P1639 fail this ignition?
--
Go to Step 5
Go to Step 4

4
Turn ON the ignition leaving the engine OFF.
Review the Freeze Frame and/or Failure Records data for this DTC and observe the parameters.
Turn OFF the ignition for 15 seconds.
Start the engine.
Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in Freeze Frame/Failure Records as possible. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running the DTC.
Select the Diagnostic Trouble Code (DTC) option, the Specific DTC option, then enter the DTC number using the scan tool.
Does the scan tool indicate the DTC set this ignition?
--
Go to Step 5
Go to Diagnostic Aids

5
Turn OFF the ignition.
Disconnect the PCM connector C1. Refer to Powertrain Control Module (PCM) Replacement .
Connect the test lamp J 34142-B to B+.
Probe the PCM connector 5 volt reference circuits for the following components:
The A/C Refrigerant Pressure sensor
The Fuel Tank Pressure sensor
Does the test lamp illuminate for any of the circuits?
--
Go to Step 7
Go to Step 6

6
Test continuity from each 5 volt reference circuit to all other PCM circuits at the PCM harness connector using the DMM. Example: probe one lead to the A/C Refrigerant Pressure sensor 5 volt reference (at the PCM harness connector) circuit and probe the other lead to each terminal at the PCM harness connector. This must be performed for each 5 volt reference circuit. Refer to Testing for Continuity in Wiring Systems.

Do any of the circuits indicate a resistance within the specified range?
0-2ohms
Go to Step 8
Go to Step 9

7
Repair the short to ground on the appropriate 5 volt reference circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?
--
Go to Step 10
--

8
Repair the short between the appropriate 5 volt reference circuit and the PCM circuit that had continuity. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?
--
Go to Step 10
--

9

Important
Program the replacement PCM.


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

Is the action complete?
--
Go to Step 10
--

10
Select the Diagnostic Trouble Codes (DTC) option and the Clear DTC Information option using the scan tool.
Start the engine and idle at the normal operating temperature.
Select the Specific DTC option under the Diagnostic Trouble Code (DTC) option using a scan tool.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text if applicable.
Does the scan tool indicate that this test ran and passed?
--
Go to Step 11
Go to Step 2

11
Select the Capture Info option and the Review Info option using the scan tool.

Are any DTCs displayed that you have not diagnosed?
--
Go to applicable DTC table
System OK



--------------------------------------------------------------------------------
Document ID# 554890
2000 Chevrolet/Geo Corvette

 

Thanks for the info Bill. Where is this connector at, they reference to in this write up?