DTC P1639 5 Volt Reference 2 Circuit. Chevrolet Monte Carlo 1998

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1998 🢒 Monte Carlo 🢒 DTC 🢒 DTC P1639 5 Volt Reference 2 Circuit

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

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	Value(s)	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	Visually/physically check the PCM and engine grounds. Refer to Ground Distribution Schematics in Wiring Systems. Was a problem found?	--	Go to Step 13	Go to Step 3
3	Ensure that the A/C is OFF. Observe A/C High Side Pressure display on the scan tool. Does the scan tool display voltage greater than the first specified value or less than the second specified value?	4.8 V 0.1 V	Go to DTC P0530 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit	Go to Step 4
4	Disconnect the A/C refrigerant pressure sensor. Using a J 39200 DMM, measure voltage between the 5 volt reference B circuit and the sensor ground circuit. Is voltage greater than the specified value?	5.5 V	Go to Step 5	Go to Step 7
5	Turn OFF the ignition switch. Disconnect the PCM. Turn ON the ignition switch. Measure voltage between the 5 volt reference B circuit and the PCM ground circuit at the PCM harness connector. Is voltage greater than the specified value indicated?	5.5 V	Go to Step 6	Go to Step 11
6	Locate and repair short to voltage in the 5 volt reference B circuit. Did you complete the repair?	--	Go to Step 13	--
7	Is voltage less than the specified value indicated?	4.5 V	Go to Step 9	Go to Step 8
8	Check for a short to voltage in the A/C refrigerant pressure sensor signal circuit wiring. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems. Was a problem found?	--	Go to Step 13	Go to Step 10
9	Turn OFF the ignition switch. Disconnect the PCM. Turn on the ignition switch. Check the 5 volt reference B circuit for a short to ground or to the sensor ground circuit. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems. Was a problem found?	--	Go to Step 13	Go to Step 11
10	Turn ON the ignition switch with the A/C pressure sensor disconnected. After at least 10 seconds, check for DTC P1635. Is DTC P1635 set?	--	Go to Step 11	Go to Step 12
11	Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the repair?	--	Go to Step 13	--
12	Replace the A/C refrigerant pressure sensor. Refer to Condenser Replacement in HVAC System-Manual. Did you complete the repair?	--	Go to Step 13	--
13	Review and record scan tool Fail Records data. Clear DTCs. Operate the vehicle within Fail Records conditions. Using a scan tool, monitor Specific DTC info for DTC P1639 until the DTC P1639 test runs. Does the scan tool indicate DTC P1639 failed this ignition?	--	Go to Step 2	System OK