2006 Buick Lucerne-Runs Hot

This 2006 Buick Lucerne came in with the complaint that the engine would run hot sometimes. The cooling fans had been replaced with used parts and the coolant reservoir had also been replaced. The customer had stated that someone told them that the oxygen sensor could be causing the problem. I told him that I doubted that but would look into it. Well it turns out that a blown oxygen sensor heater fuse can cause an overheating issue.

The fuse is labeled as OXY POST and it is at position F21.

There had been a 25 amp fuse installed and it was blown. I replaced it twice and the new fuse would blow as soon as the ignition was turned on. As luck would have it though on the third try it stopped blowing and the short was gone.

I looked at a common area where the wiring is known to short out on theses vehicles but no short was found. This harness runs along the front of the engine just below the upper radiator hose.

It took quite a while to locate the short by my diligence paid off. The short was located where the rear wiring harness turns down and goes behind a power steering line. It was rubbing on the hold down clamp that secures the line to the engine.

I had to disconnect the wiring harness from the rear oxygen sensor, the transmission output speed sensor and the right front wheel speed sensor. Disconnecting the rear oxygen sensor involved drilling out three rivets that held on a heat shield over the wiring. Finally the harness was up where it could be repaired.

A close up of the damaged pink/black wire.

The removed degraded split loom and harness tape.

The cleaned up harness with new split loom and heat resistant tape. Nothing like being wrapped up under and around a vehicle, working through a wheel well and other minor openings for a whole day fixing a tee tiny little short.

The really fun part was re installing the harness and routing it correctly. By the way even though the old split loom was degraded and left the wiring exposed for damage the real culprit in this problem was whoever had replaced the rack and pinion assembly had left it’s heat shield loose. The wiring harness is secured to the heat shield and was being moved around while the vehicle was being driven. Including gravity pulling down and causing the wire to cut into the metal hold down clamp. In nut shell old parts and poor workmanship caused this problem.  Now they just have to fix a half dozen or so other issues and the vehicle may be dependable.

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