What Does C1234 Mean?
The ABS module has detected that the left rear wheel speed sensor circuit is either open or shorted. The module cannot obtain a valid speed signal from the left rear wheel, disabling ABS and traction control functions. Dashboard warning lights for ABS and TC will be illuminated.
Common Causes
35%
Failed left rear wheel speed sensor (open or shorted winding)
30%
Damaged wiring in the left rear sensor circuit — severed, chafed, or corroded
20%
Corroded or disconnected sensor or module connector
10%
Damaged tone ring on the left rear hub or axle
5%
ABS module internal input failure for the left rear channel
Diagnostic Steps
1
Measure sensor resistance at the left rear wheel speed sensor connector — expect 800-2000 ohms. Infinite resistance indicates an open condition; near-zero resistance indicates a short.
2
Test both signal wires for shorts to ground (should be open) and shorts to battery (should show 0V) with the sensor disconnected. Any unintended continuity points to a wiring fault.
3
Inspect the left rear sensor harness routing along the rear suspension, axle, and underbody. Look for chafing on metal edges, heat damage from exhaust proximity, and road debris impact.
4
Verify the sensor is fully seated in its mounting bore and the connector is properly mated and locked. A loose sensor or connector is a frequent cause of intermittent open/short codes.
5
Perform end-to-end resistance and continuity tests from the sensor connector to the ABS module connector to pinpoint any break or short within the harness.
Estimated Repair Cost
$80 - $350
Parts + labor, varies by vehicle and location
The ABS module has detected that the left rear wheel speed sensor circuit is either open or shorted. The module cannot obtain a valid speed signal from the left rear wheel, disabling ABS and traction control functions. Dashboard warning lights for ABS and TC will be illuminated.
The most common cause of C1234 (Left Rear Wheel Speed Circuit Open or Shorted) is: Failed left rear wheel speed sensor (open or shorted winding)
Typical repair costs for C1234 range from $80 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
ABS and traction control are disabled on the left rear corner. Normal braking remains functional. Avoid aggressive braking on slippery surfaces. Safe to drive to a repair facility at moderate speed.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to C1234 to identify the root cause.
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