DTC P1639 5 Volt Reference 2 Circuit. Buick LeSabre 2000

For 1990-2009 cars only

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

Engine Controls Components
Fuel Tank Pressure Sensor, EVAP Canister Vent Solenoid
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 Running the DTC

The engine is running.

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 does not illuminate the malfunction indicator lamp (MIL).

•	The PCM stores the conditions that 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.

•	the 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:

•	A faulty 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. Use a corresponding mating terminal to test for proper terminal tension.

•

A 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 occurs that caused the DTC to set. 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 replaced, the new PCM must be programmed.

DTC P1639 - 5 Volt Reference B Circuit

Step	Action	Value(s)	Yes	No
1	Was the Powertrain On-Board Diagnostic (OBD) System Check performed?	--	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 . 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 more 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 DMM, measure voltage between the 5 volt reference B circuit and the sensor ground circuit. Is voltage more than the specified value?	5.1 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 teh voltage more than the specified value?	5.1 V	Go to Step 6	Go to Step 11
6	Locate and repair short to voltage in the 5 volt reference B circuit. Is action complete?	--	Go to Step 13	--
7	Is voltage less than the specified value indicated?	4.9 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. 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 Is the action complete?	--	Go to Step 13	--
12	Replace the A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in Heater, Ventilation, and Air Conditioning (HVAC). Is the action complete?	--	Go to Step 13	--
13	Review and record the scan tool Fail Records data. Clear the DTCs. Operate the vehicle within Fail Records conditions. Using a scan tool, monitor the 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