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Tuesday, October 16, 2018

Doug's Domain

Doug Vetter, ATP/CFI

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Thursday, June 6, 2018

ASC Throttle Body Actuator Cable Replacement

As I pulled out of the airport parking lot the other day the traction control (ASC) and anti-skid braking system (ABS) annunciators suddenly illuminated. The last time this happened I wound up doing a bit of troubleshooting with the wheel speed sensors before giving up and taking it to my technician for a diagnosis. At the time he revealed that the ASC throttle body wasn't going through its expected self test sweep shortly after the engine started and we ultimately traced that condition to a faulty ASC relay.

The next day I was scheduled to return to the airport in the afternoon so I didn't have a lot of time to screw with this problem, but I didn't really want to drive three hours with a bunch of annoying annunciators staring me in the face so I took out the ASC relay, smacked it against the top of the strut tower a few times and then reseated it. When I started the engine I noted that the ASC throttle body did not go through its self test sweep and the annunciators remained illuminated so I figured I'd head over to my dealer to talk with my tech once again.

(Image: New ASC throttle body actuator cable install)

A few miles into my journey to the dealer, however, I glanced down at the gauge cluster only to realize that the annunciators had extinguished on their own. Convinced that this was the result of either an intermittent fault or a delayed response to my "coercion" of the relay I figured I'd continue to the dealer so I could order a new relay and chat with my tech. Surprisingly they had the relay in stock so I picked it up for $27 and swapped it in the parking lot. A moment after I started the engine I noticed the throttle body actuator go through its self test sweep. I wound up canceling my afternoon flight due to thunderstorms so I never did go to the airport later that day but the errands I ran instead resulted in several drive cycles without so much as a flicker of the annunciators so I considered this job done.

Unfortunately, a couple days later I saw the lights illuminate again but extinguish on a subsequent drive cycle. Frustrated, I called my technician and he suggested dropping by his bay the following morning. Upon my arrival we did a diagnostic on the car only to find no relevant codes stored. We pulled the ASC and ABS relays to inspect the contacts and found both of those in good condition. My technician examined the wiring associated with the ASC throttle body but everything was found in good working order. We then raised the vehicle on the lift to inspect the tone rings on all four wheels and those were also found to be in good shape (i.e. not rusted and clear of debris).

And then, following a closer check of the throttle body, we found a potential smoking gun. One side of the cable that allows the ASC throttle body actuator to move the throttle body plate is terminated in a threaded plastic barrel that is normally surrounded by three barbed protrusions which secure it to a mounting flange. Unfortunately, all of the barbed protrusions had broken due to age and the cable was more or less loose in its mount. The working theory at this point was that the slack in the cable prevented a full sweep of the ASC throttle body and that was picked up by the position sensor, and hence the DME, which then illuminated the ASC and ABS warning lights.

I later ordered a new cable and installed it myself today in about an hour including setup (lighting for video, etc.) After everything was reinstalled I started the engine and saw the ASC throttle body go through its self test with a full sweep so I think this has solved the problem but I will have to wait several drive cycles before I'm sure. If the problem persists the next most likely cause is the position sensor but as that is about $100 my cost I don't want to replace it unless absolutely necessary. Total cost for this repair was about $100 including a small tip for my tech so I figured I came out ahead.

Video: ASC Throttle Body Actuator Cable Replacement Highlights

Mileage: 270070