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Dan
Dan, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1555
Experience:  Auto Technician
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2002 chev astro. my abs light is on and sometimes brake

Customer Question

2002 chev astro. my abs light is on and sometimes brake light. When both are on, the transmission quits working, along with the speedometer. I took original abs module off and put on dorman replacement. Then a bunch of lights came on. One was the speed sensor on the transmission I replaced the trans speed sensor and the light came back on and trans went out. Ordered another abs module and the light went out for 4 test trips. Now it's back on and the brake light flashed. Almost back to where I started. I'm getting a CO265 error, CO245, co267, and co237. As near as I can tell, there is no rear wheel speed sensor. My mechanic and I both checked. I'm at whits end.
JA: Is it just the ABS light? Or is the brake system warning light on, too?
Customer: The ABS light came on and stayed, and the brake light flashed and went out, for now
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Well, I changed out the ABS module twice, and the mechanic changed the transmission speed sensor (VSS). Now lights back on.
JA: Anything else you think the mechanic should know?
Customer: Can't see any rear wheel speed sensor, myself or mechanic. I have a hard time thinking the original and 2 rebuilt Dorman ABS modules are all bad. I have cleared the codes after each new ABS, and R/R negative brake cable
Submitted: 5 months ago.
Category: Chevy
Expert:  Dan replied 5 months ago.

Hello my name is***** am an ASE Master Technician and I am glad to help you out with your question.

Expert:  Dan replied 5 months ago.

It does not have rear speed sensor. Only has the one on the trans.

Customer: replied 5 months ago.
but it keeps coming up with co237 errors. I have replaced the abs module twice and the transmission speed sensor once. same errors appear, now co265, co245, co267, co237
Expert:  Dan replied 5 months ago.

c0237

DTC C0235: Rear Wheel Speed Signal Circuit Open; C0236: Rear Wheel Speed Signal Circuit Missing; C0237: Rear Wheel Speed Signal Erratic; P1504: Vehicle Speed Output Circuit

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 & 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. Refer to TESTING FOR ELECTRICAL INTERMITTENTSTESTING FOR ELECTRICAL INTERMITTENTS , TESTING FOR INTERMITTENT & POOR CONNECTIONS , WIRING REPAIRS and CONNECTOR REPAIRS .

Test Description

The numbers below Refer to the step numbers on the diagnostic table.

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

DTC C0235-C0237 Or P1504 Diagnosis

StepActionValuesYesNo

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

2

  1. 1) Use a scan tool in order to clear the DTCs.
  2. 2) Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC set?-Go to Step 3 Diagnostic Aids3

  1. 1) Turn OFF the ignition.
  2. 2) Disconnect from the EBCM, the harness connector containing the vehicle speed signal circuit.
  3. 3) Turn ON the ignition.
  4. 4) Use a DMM in order to measure the DC voltage between the vehicle speed signal circuit and a good ground.

Does the voltage measure greater than the specified value?10 VoltsGo to Step 4 Go to Step 7 4

  1. 1) Raise and support the vehicle.
  2. 2) Place the transmission in neutral (N)
  3. 3) Set up the DMM in order to measure the DC voltage between the vehicle speed signal circuit and a good ground.
  4. 4) Spin the rear wheels as fast as possible by hand for at least 30 seconds and while ensuring the driveshaft is rotating, observe the DMM.

Does the voltage measure within the specified range the entire time the driveshaft is rotating?5-7VoltsGo to Step 5 Go to Step 7

5Inspect for poor connections at the harness connector of the EBCM. Refer to TESTING FOR INTERMITTENT & POOR CONNECTIONS and CONNECTOR REPAIRS . Did you find and correct the condition?-Go to Step 10 Go to Step 6

6Important: Following EBCM replacement, use the scan tool to perform the Tire Size Calibration procedure. Replace the EBCM. Refer to ELECTRONIC BRAKE CONTROL MODULE (EBCM) REPLACEMENT . Did you complete the replacement?-Go to Step 10 -

7Test the vehicle speed signal circuit for an open, a short to ground or a short to voltage. Refer to CIRCUIT TESTING and WIRING REPAIRS . Did you find and correct the condition?-Go to Step 10 Go to Step 8

8Inspect for poor connections at the harness connector of the PCM. Refer to TESTING FOR INTERMITTENT & POOR CONNECTIONS and CONNECTOR REPAIRS . Did you find and correct the condition?-Go to Step 10 Go to Step 9

9Important: Perform the setup procedure for the PCM. Replace the PCM. Refer to POWERTRAIN CONTROL MODULE . Did you complete replacement?-Go to Step 10 -

10

  1. 1) Use the scan tool in order to clear the DTC.
  2. 2) Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?-Go to Step 3 System OK

Expert:  Dan replied 5 months ago.

Have you gone through the diagnostic steps?

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