DTC B2648 Ambient Light Sensor Circuit High

i had my twilight lights turned on with a tech2, and whenever they are on the lights are on light or dark. they do shut off automatically. just don't come up at the right time. any ideas...

if i can't get it resolved i will probably just have it turned off.

 

You might want to replace the ambiant light sensor.It is located in the grill on the top of the dash.The grill simply pops out...

 

should this work though is more of my question. Z06's don't come with this but i saw gtp did this in his post and i am wondering if this is a side affect?
http://forums.corvetteforum.com/zerothread?&id=323745

any thoughts...

 

Interesting,

I've done this mod on a few cars now and never got this problem. C5-TECH.....what does the ZO6 normally use this light sensor for since it does'nt come with this feature? Its my understanding the rearview mirror has the light sensor for electrochromatic mirrors and the HUD has its own light sensor for adjusting brightness.

Aaron Lephart

 

ttt

 

DTC B2648

Circuit Description
The ambient light sensor circuit provides an input to the BCM for DRL and automatic headlight functions. This input allows the BCM to activate or deactivate DRL and automatic headlamps with different ambient light levels. The BCM supplies a 5 volt reference circuit and a signal circuit to the ambient light sensor. The BCM will detect high voltage on the ambient light sensor signal circuit when ambient light is high, and low voltage when ambient light is low. The BCM monitors the ambient light sensor voltage at the signal circuit and determines if the voltage is within range. If the voltage is not within range, a malfunction is present and a DTC will set.

Conditions for Setting the DTC

A short to voltage in the ambient light sensor circuit.
Condition must be present for 2 seconds.

Action Taken When the DTC Sets

Stores a DTC B2648 in the BCM memory.
The automatic headlamps and park lamps will remain ON.
Conditions for Clearing the DTC
The BCM no longer detects a short to voltage in the ambient light sensor circuit.
A history DTC will clear after 50 consecutive ignition cycles if the condition for the malfunction is no longer present.
Use the IPC clearing DTCs feature.
The BCM receives the Clear Code command from the scan tool.

Diagnostic Aids

The following conditions may cause an intermittent malfunction:
An intermittent short to voltage in the ambient light sensor signal circuit.
An intermittent short to voltage in the ambient light sensor reference circuit.
If the ambient light sensor circuit is open or shorted (to ground or voltage), the BCM will command the automatic headlamps and park lamps ON. If the ignition is cycled the BCM will retest for any malfunctions in the ambient light sensor circuit and if a malfunction is current the BCM will activate the automatic.
If the DTC is a history DTC, the problem may be intermittent. Perform the tests shown while moving related wiring and connectors. This can often cause the malfunction to occur. Refer to Testing for Intermittent and Poor Connections in Wiring Systems.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.

Tests ambient light sensor data using a scan tool.

Tests the ambient light sensor data with the sensor disconnected. The scan tool will display ambient light sensor voltage as 0 volts with the sensor disconnected.

Tests the ambient light sensor data with a jumper wire between the reference and signal circuit. The scan tool will display ambient light sensor voltage between 3.5-4.5 volts with the sensor jumpered.

Tests for a short to voltage in the 5 volt reference circuit.

Step
Action
Value(s)
Yes
No

Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics

1
Did you perform the Lighting System Diagnostic System Check?
--
Go to Step 2
Go to Diagnostic System Check - Lighting Systems

2
Install a scan tool.
Turn ON the ignition, with the engine OFF.
Apply a bright incandescent light to the ambient light sensor.
With a scan tool, observe the DRL Ambient Light Sensor parameter in the BCM data list.
Does the scan tool indicate that the DRL Ambient Light Sensor parameter is within the specified range?
0.1-2.5 V
Go to Diagnostic Aids
Go to Step 3

3
Turn OFF the ignition.
Disconnect the ambient light sensor.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the DRL Ambient Light Sensor parameter.
Does the scan tool indicate that the DRL Ambient Light Sensor parameter is less than the specified value?
0.1 V
Go to Step 4
Go to Step 9

4
Turn OFF the ignition.
Connect a 3 amp fused jumper wire between the 5 volt reference circuit of the ambient light sensor and the signal circuit of the ambient light sensor.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the DRL Ambient Light Sensor parameter.
Does the scan tool indicate that the DRL Ambient Light Sensor parameter is greater than the specified value?
3.5 V
Go to Step 5
Go to Step 7

5
Disconnect the fused jumper wire.
Measure the voltage between the 5 volt reference circuit of the ambient light sensor and the signal circuit of the ambient light sensor.
Does the voltage measure less than the specified value?
5.0 V
Go to Step 10
Go to Step 6

6
Test the 5 volt reference circuit of the ambient light sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 14
Go to Step 11

7
Test the 5 volt reference circuit of the ambient light sensor for a short to ground, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 14
Go to Step 8

8
Test the signal circuit of the ambient light sensor for a short to ground, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 14
Go to Step 11

9
Test the signal circuit of the ambient light sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 14
Go to Step 11

10
Inspect for poor connections at the harness connector of the ambient light sensor. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 14
Go to Step 12

11
Inspect for poor connections at the harness connector of the BCM. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 14
Go to Step 13

12
Replace the ambient light sensor. Refer to Daytime Running Lamps (DRL) Ambient Light Sensor Replacement .

Did you complete the replacement?
--
Go to Step 14
--

13

Important
Perform the BCM reprogram procedure. Refer to Body Control Module (BCM) Programming/RPO Configuration in Body Control System.


Replace the BCM. Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?
--
Go to Step 14
--

14
Use the scan tool in order to clear the DTCs.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC reset?
--
Go to Step 2
System OK

 

thanks man, you are the best. i will print this out and get this resolved when i get back into town.