DTC P1639 5 Volt Reference 2 Circuit. Buick Regal 2000

For 1990-2009 cars only

Makes 🢒 Buick 🢒 2000 🢒 Regal 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P1639 5 Volt Reference 2 Circuit

Engine Controls Components
A/C Pressure Switch, Throttle Position Sensor, MAP Sensor, ECT Sensor and IAT Sensor
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The powertrain control module (PCM) uses the 5 Volt Reference B circuit as a sensor feed for the A/C refrigerant pressure sensor and the fuel tank pressure sensor. The PCM monitors the voltage on the 5 Volt Reference B circuit. If the voltage is out of tolerance, DTC P1639 will set.

Conditions for Setting the DTC

•	The PCM detects a voltage out of tolerance condition on the 5 Volt Reference B 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: Inspect the PCM and engine grounds for being secure and clean.

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.

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

Values

Yes

Did you perform the Powertrain On Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Visually and physically 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.

Did you find and correct the condition?

Go to Step 12

Go to Step 3

Turn OFF the ignition.
Disconnect the fuel tank pressure (FTP) sensor connector.
Turn ON the ignition, leaving the engine OFF.
Connect a DMM between the 5 Volt Reference and sensor ground in the FTP sensor connector.

Does the voltage measure more than the specified value?

5 V

Go to Step 4

Go to Step 5

Leave the DMM connected.
Turn OFF the ignition.
Disconnect the PCM connector.
Turn ON the ignition, with the engine OFF.

Does the voltage measure more than the specified value?

5 V

Go to Step 8

Go to Step 11

Does the voltage measure less than the specified value?

5 V

Go to Step 6

Go to Step 9

Leave the DMM connected to the 5 Volt Reference and sensor ground circuits at the FTP connector.
Disconnect the A/C pressure sensor connector.

Does the voltage measure near the specified value?

5 V

Go to Step 10

Go to Step 7

Turn OFF the ignition.
Leave the FTP and the A/C pressure sensors disconnected.
Disconnect the PCM connector.
Test the 5 Volt Reference for a short to chassis or sensor ground.
If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 11

Locate and repair the short to voltage in the following circuits:

•	5 Volt Reference circuit

•	FTP Sensor signal circuit

•	A/C Pressure Sensor signal circuit

Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 12

Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement .

Is the action complete?

Go to Step 12

Replace the A/C pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in Heating, Ventilation, and Air Conditioning.

Is the action complete?

Go to Step 12

Important: The replacement PCM must be reprogrammed.

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

Is the action complete?

Go to Step 12

Use a scan tool to clear the DTCs.
Operate the vehicle within the Conditions for Setting the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 3

System OK