DTC P1639 5 Volt Reference 2 Circuit. Pontiac Grand Prix 1999

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 1999 🢒 Grand Prix 🢒 DTC 🢒 DTC P1639 5 Volt Reference 2 Circuit

Engine Controls Components
OBD II Symbol Description Notice
Cell 21: Engine Data Sensors-A/C Refrig Press, TP, MAP, ECT, IAT
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The 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, 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 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 Wiring Repairs .

Was a problem found?

Go to Step 12

Go to Step 3

Turn OFF the ignition switch.
Disconnect the fuel tank pressure (FTP) sensor connector.
Connect 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