Thanks to our Partner, NAPA Autotech Training

Key Points & Takeaways:

The Problem:

• A 2023 Jeep Grand Cherokee (collision repair) came in with blind spot warning and parking aid malfunction lights on.
• No functionality in either system post-repair.

Initial Diagnosis:

• Verified the concern (instrument cluster lit up with warnings).
• Used an aftermarket scan tool (Snap-on Ultra) and found:
• ADAS control module had multiple DTCs for open/short circuits on all radar sensors.
• Parking aid module had similar codes for ultrasonic sensors.
• Vehicle was hit in the passenger rear, leading to replacement of the bumper, harness, and rear hatch.

Suspected Causes:

• Blown fuse (common culprit for multiple system failures).
• Crushed/damaged wiring harness (common after collisions).
• Module failure due to impact.

Testing & Findings:

• Checked power and ground at the ADAS module—all good.
• Inspected wiring harness for damage (no visible issues).
• Critical Clue: Wire colors didn’t match the schematic.
• Initially dismissed as a common schematic error.
• Later realized the entire harness was installed backward (left/right sides flipped).

The Fix:

• Flipped the harness and radar modules to their correct positions.
• All codes cleared except two for the blind spot radars—turned out they were also swapped.
• After correction, all systems worked perfectly.

Lessons Learned:

• Don’t get stuck in a diagnostic rabbit hole. Good techs pivot when clues don’t add up.
• Man-made problems can be the trickiest. Always verify previous work (especially after collisions).
• Wire color discrepancies matter. Even if schematics are often wrong, they can reveal bigger issues.
• "Slow down to speed up." Rushing leads to wasted time; methodical checks save hours.

Final Thoughts:

• Awareness is key. Catch yourself when fixating on one theory.
• Experience can work against you. Stay open to new clues, even if they conflict with past patterns.

Contact Information

• Email Matt: mattfanslowpodcast@gmail.com
• Diagnosing the Aftermarket A - Z YouTube Channel
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Diagnosing the Aftermarket A to Z with Matt Fanslow: From Diagnostics to Metallica and Mental Health, Matt Fanslow is Lifting the Hood on Life. https://mattfanslow.captivate.fm/

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