DTC B2647 Ambient Light Sensor Circuit Low. Chevrolet Chevy C Silverado

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1999 🢒 Chevy C Silverado - 2WD 🢒 DTC 🢒 DTC B2647 Ambient Light Sensor Circuit Low

Body Control Module Components
Body Control System Schematics
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The body control module (BCM) monitors CKT 278 in order to determine if the daytime running lights (DRL) or the auto headlights (AHL) should be turned ON in the AUTO mode. When the BCM senses the ambient light sensor voltage between 1.7-4.7 volts (light state) the DRL will be commanded ON. When the BCM senses the ambient light sensor voltage between 0.2-1.0 volts (park state) the AHL will be commanded .

Conditions for Setting the DTC

•	When the ambient light sensor input voltage is less than 0.2 volts (CKT 278 is open or shorted to ground).

•	The system voltage must be between 9.0-16.0 volts.

•	The above conditions must be met for 0.5 seconds

Action Taken When the DTC Sets

The AHL will remain ON in any ambient light state.

Conditions for Clearing the MIL/DTC

•	This DTC will clear immediately after the condition for setting the fault is corrected.

•	A history DTC will clear after 100 consecutive ignition cycles without a fault present.

•	Use a scan too in order to clear history and current DTCs.

Diagnostic Aids

•	Always perform the first DTC listed on the scan tool if more than 1 DTC is displayed.

•	The scan tool must display DTC B2647 as a current code before performing diagnostics.

•	Perform a visual inspection for loose or poor connections at all related components.

•	Refer to Intermittents and Poor Connections Wiring Systems.

Test Description

Step number(s) below refer to the same step number(s) in the Diagnostic Table.

This step tests the ambient light sensor CKT 278 for an open.

This step tests the ambient light sensor CKT 278 for a short to ground.

Step	Action	Value(s)	Yes	No
1	Was the BCM Diagnostic System Check performed?	--	Go to Step 2	Go to Diagnostic System Check - Body Control System
2	Turn the ignition switch to the RUN position. Place a trouble light by the ambient light sensor in order to increase the voltage on CKT 278. Backprobe with the J 39200 digital multimeter (DMM) and measure the voltage between CKT 278 (WHT) cavity A6 of the purple BCM (C3) connector and ground. Is the voltage within the specified values?	1.1-4.7 volts	Go to Step 10	Go to Step 3
3	Turn the ignition switch to the OFF position. Disconnect the ambient light sensor. With a J 39200 DMM, measure the resistance between the ambient light sensor CKT 278 (WHT) cavity B to the BCM (C3) connector cavity A6. Is the resistance within the specified range?	0-5ohms	Go to Step 4	Go to Step 7
4	Connect a test lamp to B+ and probe the ambient light sensor CKT 278 (WHT) cavity B. Does the test lamp light?	--	Go to Step 8	Go to Step 5
5	With a J 39200 DMM, measure the resistance between the ambient light sensor CKT 705 (GRY) cavity A and the purple BCM (C3) connector cavity A4 . Is the resistance within the specified range?	0-5ohms	Go to Step 9	Go to Step 6
6	Locate and repair the open GRY (705) wire between the ambient light sensor and the BCM. Is the repair complete?	--	Go to Step 11	--
7	Locate and repair the open in CKT 278 (WHT) between the ambient light sensor and the BCM. Is the repair complete?	--	Go to Step 11	--
8	Locate and repair short to ground on CKT 278 (WHT) between the ambient light sensor and the BCM? Is the repair complete?	--	Go to Step 11	--
9	Replace the ambient light sensor. Is the repair complete?	--	Go to Step 11	--
10	Replace the BCM. Refer to Body Control Module Replacement . Program the BCM with the proper calibrations. Refer to Body Control Module (BCM) Programming/RPO Configuration . Perform the learn procedure. Is the repair complete?	--	System OK	--
11	Clear the DTCs. Refer to Clearing DTCs . Is the action complete?	--	System OK	--