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2017 Terrain SLT ABS/Traction Control Lights On, Erratic Speedo

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James R. · rep 0 · May 22, 3:41 AM · 1 replies · solved · Question

Vehicle: 2017 GMC Terrain SLT

Hello everyone,

I'm having a really annoying and potentially dangerous issue with my 2017 GMC Terrain SLT, 2.4L engine. For the past few days, the ABS warning light and the Traction Control warning light have both been illuminated on my dash. On top of that, my speedometer has started acting erratically – sometimes it drops to zero while I'm driving, then jumps back up, or just gives a completely wrong reading.

I've also noticed a few other weird electrical glitches, like the radio cutting out for a second or the interior lights flickering. I checked the battery terminals, and they seem clean and tight. I'm worried this is more than just a sensor. Could it be a wheel speed sensor, or something bigger like the BCM?

Any advice on where to start looking? It's making me nervous to drive.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:41 AM

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ClearTheCode admin answer:

The combination of illuminated ABS and Traction Control lights, an erratic speedometer, and other electrical glitches on your 2017 GMC Terrain SLT strongly suggests a problem with the wheel speed sensors or the vehicle's electrical system, specifically related to the Anti-lock Brake System (ABS) module or wiring.

Here's a breakdown of the most likely causes and diagnostic steps:

  1. Wheel Speed Sensors (WSS):
    • Faulty Sensor: A failing wheel speed sensor is a very common cause for ABS/Traction Control lights. If one sensor is sending incorrect or intermittent data, the ABS module can't accurately determine wheel speed, leading to system deactivation and an erratic speedometer (as the speedometer often gets its signal from a WSS).
    • Damaged Wiring: The wiring harness to a wheel speed sensor can get damaged by road debris, corrosion, or even during brake jobs. Inspect the wiring at each wheel for cuts, fraying, or loose connections.
    • Dirty Sensor/Tone Ring: Debris or metallic shavings on the sensor tip or the magnetic tone ring (which the sensor reads) can interfere with its signal.
  2. ABS Module Failure:
    • While less common than a sensor, the ABS control module itself can fail. Internal circuit board issues can lead to a loss of communication or incorrect processing of sensor data, causing all the symptoms you describe.
  3. Grounding Issues/Electrical System Problems:
    • The flickering lights and radio cut-outs, combined with the other issues, could point to a broader electrical problem, such as a poor ground connection, a failing alternator (though you'd likely see a battery light), or a weak battery (even if terminals are clean, internal battery health can be poor).
  4. Body Control Module (BCM):
    • The BCM manages many electrical functions. While less likely to directly cause ABS/speedometer issues without other widespread problems, a faulty BCM could contribute to the general electrical glitches.

When to see a shop:

  • Immediately: Driving with compromised ABS and Traction Control can be unsafe, especially in adverse conditions. The erratic speedometer also makes it difficult to judge your speed accurately.
  • For Diagnosis: A professional shop can use an advanced scan tool to:
    • Read specific ABS/Traction Control codes (which are different from standard OBD-II engine codes).
    • Monitor live data from each wheel speed sensor to identify which one is faulty or intermittent.
    • Perform diagnostic tests on the ABS module and check for proper communication between modules.
    • Thoroughly inspect wiring and ground points throughout the vehicle's electrical system. Pinpointing the exact cause of these interconnected issues requires specialized diagnostic equipment and expertise.
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