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Technician Chris
Technician Chris, Technician
Category: Car
Satisfied Customers: 365
Experience:  I am a certified ASE Master Technician with L1 Advanced Diagnostic Specialist and over 15 years experience.
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GM silverado 1500: Abs and parking brake light flashes...and

Resolved Question:

Abs and parking brake light flashes...and a code of c0237 and c0265...the truck some time neutralize by it self and when my mph reach about 50 the parking brake light flash and the abs light turns on....this started to do it when my drive shaft broke and the tail of the transmission broke so I replace everything with new vss..any suggestions what could be causing this problem?
Submitted: 10 months ago.
Category: Car
Expert:  Technician Chris replied 10 months ago.

Most likely you have an open wire in the ABS circuit, but see below for the pinpoint test procedure for each code, you will need to measure voltage using a DMM.

 

C0237:

 

graphic

 

graphic

 

 

Steps 4 of 10

 

Circuit Description
The PCM converts the data from the vehicle speed sensor to a 128k pulses/mile signal. The EBCM uses the vehicle speed signal from the PCM in order to calculate the rear wheel speed.

Conditions for Running the DTC
C0235
The ignition is ON.

C0236 and C0237

  • The ignition is ON.
  • The vehicle speed is greater than 32 km/h (20 mph) when the brake is applied or 19 km/h (12 mph) when the brake is released.

P1504

  • The ignition is ON.
  • The vehicle is not moving.

Conditions for Setting the DTC
C0235
The EBCM detects low voltage on the vehicle speed signal circuit for 500 milliseconds.

C0236
The rear wheel speed signal is less than 6 km/h (4 mph) for 5 seconds, or 120 seconds in order to set multiple missing sensor signal DTCs.

C0237
The EBCM detects an erratic rear wheel speed signal for 105 milliseconds.

P1504
The PCM detects low voltage on the vehicle speed signal circuit for 45 seconds.

Action Taken When the DTC Sets
If equipped, the following actions occur:

  • The EBCM disables the ABS/TCS/DRP.
  • The ABS indicator turns ON.
  • The TRACTION OFF indicator turns ON.
  • The red brake warning indicator turns ON.

Conditions for Clearing the DTC

  • Repair the condition responsible for setting the DTC.
  • Use a scan tool in order to clear the DTC.
  • After the DTC is cleared and the ignition is ON, the ABS indicator may remain ON until the EBCM completes a power-up self-test. This test concludes when the vehicle reaches a speed greater than 13 km/h (8 mph) and the wheel speeds are verified by the EBCM.

Diagnostic Aids
Thoroughly inspect connections or circuitry that may cause an intermittent malfunction.

Test Description
The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests for a voltage signal from the PCM.
  2. This step tests for a missing or erratic vehicle speed signal from the PCM. An assistant may be required to perform this test.

 


C0265:

 

 

 

Steps 6 of 11

Circuit Description The ABS relay supplies battery voltage to six valve solenoids. The EBCM microprocessor applies the grounds needed to activate each solenoid. The low side of each solenoid coil has a feedback circuit to the EBCM microprocessor. When a solenoid is commanded OFF, the feedback voltage is high. When a solenoid is commanded ON, the feedback voltage is low.
Conditions for Running the DTC

  • The ignition is ON.
  • The vehicle speed is greater than 6 km/h (4 mph).

Conditions for Setting the DTC The EBCM detects an internal malfunction.
Action Taken When the DTC SetsC0265 If equipped, the following actions occur:

  • The EBCM disables the DRP/ABS.
  • The ABS indicator turns ON.
  • The brake warning indicator turns ON.

C0266 If equipped, the following actions occur:

  • The EBCM disables the ABS
  • The ABS indicator turns ON.

Conditions for Clearing the DTC The conditions for setting the DTC are no longer present and you use the scan tool Clear DTCs function.
Diagnostic Aids
Important: Whenever the EBCM is replaced for DTC C0265 or C0266, the ABS pump motor and motor circuitry must be tested for the proper resistance. Refer to steps 7 and 8 in the diagnostic table below for testing procedures and resistance values.
C0265 Thoroughly inspect connections and circuitry that may cause an intermittent malfunction.
C0266 Replace the EBCM if DTC C0266 continues to set intermittently.
Test Description The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests if the battery positive voltage circuit can supply adequate power to the system relay.
  1. A shorted ABS pump motor or shorted motor circuitry may damage the contacts within the system relay. Follow this step to prevent damage to a replacement EBCM.
Expert:  Technician Chris replied 10 months ago.

I'm sorry you are not happy w/ my answer, but this is how a tech would proceed with diagnosing your vehicle's issue. This is straight out of the Chevy repair manual. Do you have a follow up question? If so, I will be happy to assist further. I must ask that you change my rating, as it affects me greatly. The ratings are how my customers see my service level, and even just 1 negative rating is a huge deal. Please reconsider my rating. You may continue to post questions after giving me a positive rating, so please do change that.

 

Thanks

- Chris

Chevy dealer technician

Technician Chris, Technician
Category: Car
Satisfied Customers: 365
Experience: I am a certified ASE Master Technician with L1 Advanced Diagnostic Specialist and over 15 years experience.
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