DTC P1639 5 Volt Reference 2 Circuit. Chevrolet Monte Carlo 1999

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1999 🢒 Monte Carlo 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P1639 5 Volt Reference 2 Circuit

Refer to

Cell 21: Engine Data Sensors-A/C Refrig Press, TP, MAP, ECT, IAT

Engine Controls Components
Powertrain Control Module Description
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
OBD II Symbol Description Notice
Cell 21: Fuel Injectors
Cell 21: Engine Data Sensors-HO2S 1, HO2S 2
Cell 81: Instrument Cluster w/Analog Speedometer 1 of 4
Cell 21: Engine Data Sensors-MAF, EVAP Vent, EVAP Purge, EGR
Cell 21: Engine Data Sensors-Automatic Transaxle TCC Switch
Cell 21: Fuel Controls
Cell 21: Fuel Controls
Cell 21: Engine Data Sensors-MAF, EVAP Vent, EVAP Purge, EGR

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 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.

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 A/C Pressure Sensor.
Turn ON the ignition.
Connect J 39200 digital multimeter (DMM) between the 5V reference and sensor ground in the A/C Pressure Sensor connector.

Is the voltage greater than the specified value?

Go to Step 4

Go to Step 5