DTC P1639 5 Volt Reference 2 Circuit. Oldsmobile Intrigue 1998

For 1990-2009 cars only

Makes 🢒 Oldsmobile 🢒 1998 🢒 Intrigue 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P1639 5 Volt Reference 2 Circuit

Engine Controls Components
Engine Data Sensors-A/C Refrig Press, TP, MAP, ECT, IAT
OBD II Symbol Description Notice

Circuit Description

The PCM uses the 5 Volt Reference B circuit as a sensor feed for the following sensors:

•	A/C Refrigerant Pressure Sensor

•	Fuel Tank Pressure Sensor

The PCM monitors the voltage on the 5 Volt Reference B circuit. If the voltage is out of tolerance, the PCM will set DTC P1639.

Conditions for Setting the DTC

•	The PCM detects a voltage out of tolerance condition on the 5 Volt Reference B circuit.

•	Above condition for longer than 10 seconds.

Action Taken When the DTC Sets

•	The PCM will not illuminate the Malfunction Indicator Lamp (MIL).

•	The PCM will store conditions which were present when the DTC set as Fail Records data only. This information will not be stored as Freeze Frame data.

Conditions for Clearing the MIL/DTC

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

•	DTC can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.

Diagnostic Aids

Important: Inspect the PCM and engine grounds for being secure and clean.

Check for the following conditions:

•	Poor connection at the PCM.

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

•	Damaged harness.

Inspect the wiring harness for damage. If the harness appears to be OK, observe the A/C pressure display on the scan tool while moving connectors and wiring harnesses related to the A/C refrigerant pressure sensor. A change in the A/C pressure display will indicate the location of the malfunction.

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

Number(s) below refer to the step number(s) 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 P1639 - 5 Volt Reference B Circuit

Step

Action

Value(s)

Yes

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to the Powertrain On Board Diagnostic (OBD) System Check

Visually physically check the PCM and engine grounds. Ensure that the grounds are clean and secure.
If a problem is found, repair as necessary. Refer to Repair Procedures in Wiring Repairs .

Was a problem found?

Go to Step 12

Go to Step 3

Turn the ignition switch to the OFF position.
Disconnect the fuel tank pressure (FTP) sensor connector.
Connect J 39200 digital multimeter (DMM) between the 5V reference and sensor ground in the FTP sensor connector.

Is the voltage greater than the specified value?

Go to Step 4

Go to Step 5

Leave the DMM connected.
Turn the ignition switch to the OFF position.
Disconnect the PCM connector.
Turn the ignition switch to the ON position.

Is the voltage greater than the specified value?

Go to Step 8

Go to Step 11

Is the voltage less than the specified value?

Go to Step 6

Go to Step 9

Leave the DMM connected to the 5V reference and sensor ground circuits in the FTP connector.
Disconnect the A/C pressure sensor connector.

Is the voltage near the specified value?

Go to Step 10

Go to Step 7

Turn the ignition switch to the OFF position.
Leave the FTP and the A/C pressure sensors disconnected.
Disconnect the PCM connector.
Check the 5V reference for a short to chassis or sensor ground.
If a problem is found, repair as necessary. Refer to Repair Procedures in Wiring Repairs .

Was a problem found?

Go to Step 12

Go to Step 11

Locate and repair the short to voltage in the following circuit(s):

•	5V reference circuit.

•	FTP Sensor signal circuit

•	A/C Pressure Sensor signal circuit

Refer to Repair Procedures in Wiring Repairs .

Is action complete?

Go to Step 12

Replace the FTP sensor Fuel Tank Pressure Sensor Replacement .

Is action complete?

Go to Step 12

Replace the A/C Pressure Sensor. Refer to Heating, Ventilation, and Air Conditioning.

Is action complete?

Go to Step 12

Replace the PCM.

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

Is action complete?

Go to Step 12

Review and record scan tool Fail Records data.
Clear the DTCs.
Operate the vehicle within the Fail Records conditions.
Using the scan tool, monitor Specific DTC info for DTC P1639.

Does the scan tool indicate that DTC P1639 failed this ign?

Go to Step 3

System OK