Whenever somebody wants us to apply our expertise to give them peace of mind, it would be nice if we were able to offer a 100 percent guarantee, but no matter how good we think we are, time and chance can always get the upper hand. About 30 years ago, a relative of mine brought me his early 80s VW Rabbit for an inspection – he was taking it on a fairly long trip, and so I gave it the once over. I did most all of the maintenance on this vehicle, so I had carnal knowledge of the car, and I could find nothing wrong with it on my inspection.
| 2003 Grand Cherokee |
| 198,547 miles |
| 4.0LL Engine |
| 42RE Transmission |
| Complaint: "My brakes pulsate sometimes even after I let off the brakes." |
While he was on his trip, the alternator died, and a shop down in Florida charged him $300 to diagnose and replace it, which was highway robbery in those days. When he returned from the trip, he chastised me because I didn’t tell him the alternator was going to fail. Yeah, I know. I rolled my eyes too. I suppose if I had replaced the alternator, the starter, the battery, and who knows what all else, I could have averted the breakdown, but at what cost?
I remember my dad telling me about a very demanding elderly widow who came to his shop and told him she wanted him to do a comprehensive inspection of her vehicle every month and she would pay him generously each time. She then told him that if he agreed, anything that ever went wrong with her car would be 100 percent his fault and she would expect it to be repaired free of charge. He refused to even touch her car, and sent her on her way in search of a sucker, which he wasn’t. Gotta love those folks who want us to “own” all of their future problems, right?
Recently, a young woman who is just beginning her adult life brought a vehicle to me so I could “look it over” to see what I thought of it before she bought it. I’m always kind of nervous in situations like this, because a used car is, after all, a used car, and we all know that no inspection we can do for free goes deep enough to give a 100 percent guarantee of anything.
In this case, I checked all the fluid levels, perused it above and below for leaks of any kind, checked the age, pressure and condition of the tires, examined brakes and suspension parts, all of which looked fine, but I had to kill a large and healthy brown widow spider that had webbed the area just inside the right rear wheel and was waiting for a kill. There wasn’t much rust on the non-coated undercar components, so this car must have spent its life away from the coast and far enough south to avoid salt. I was most concerned about the timing belt, because that 2.7L isn’t a free-spinning engine, and with just over 100K on the clock, I decided to remove the upper part of the cover to have a look. Yeah, I know it’s usually difficult to look at a timing belt and say for sure how old it is, but this one had bright white part numbers on it and there was even a sticker on the shock tower proudly announcing the recent mileage at which the timing belt had been replaced. That put my timing belt fears to rest, and after checking for obvious electrical problems, I rounded out my inspection with a rubber stamp. The car seemed fine as far as I could tell
She thanked me for the free inspection, bought the car, and drove it for about two weeks, and then one day I was at lunch when she called to tell me that the engine had stopped running, and that she had coasted off to the side of the road. As I questioned her about it over the phone, she said the engine would spin but wouldn’t start. I told her we’d get the car to the shop after lunch and have a look at it.
Her folks decided to take it to a shop they liked to use (I do not know this shop or the man who runs it), and after changing a couple of parts and charging them a Ben Franklin or two for those fruitless attempts, he pulled the entire timing cover and said pieces of an old timing belt were trapped in there and had caused damage to the wiring. Then a couple of days later she told me he had called to say that the engine was locked up and he wanted eleven more Ben Franklins to replace it.
Busy times
My people are predictably happy when we have plenty of work. This time around it’s transmissions, brakes and steering/suspension, and we’ve had quite a lot of it. I had a couple of guys doing a go-through on a 4L60E as a bench job just for the experience of tearing it down and reassembling it, then I surprised them by having them stuff it in a 2001 Chevy trainer truck we have on hand just to see if it’d pull. It didn’t, and all the pressures were low. They ran some tests before reinstalling the original transmission with the notion that they’d tear down and re-evaluate the one that didn’t work. We also had a 2004 Dodge Stratus with an incorrect gear ratio in 3rd gear code, and that one’s still under way – it performed okay on the test drive except for a chatter on the 1-2 shift, so it’s coming back out to tear down and re-check for proper assembly.
We’ve done enough brake jobs over the past few weeks to fill my “old brake pads” bucket to capacity, and wheel alignments have been numerous and instructive. We’ve replaced multiple sets of ball joints, steering racks, pumps, leaking lines and even a front differential chunk. We had a park brake problem on a ‘91 cream puff Miata – the brake cables had been replaced by a shop in another town, but the park brakes kept getting loose, so we adjusted them the right way. We had the red ’71 Eldorado convertible back in the shop with a steering pull and a pop noise when backing up that turned out to be worn idler arm.
Then there was the wild card – a Dodge Durango that was shifting erratically and had one headlight that was going off at random – and it was off most of the time. The customer brought us a headlight connector, because when he replaced the bulb the problem remained. A simple transmission service took care of the erratic shift, and the headlight problem turned out to be in the BCM, which is totally responsible for the headlamps. I found him a replacement module on eBay.
The Jeep “brake” problem
Our title vehicle came in for an alignment and what the driver described as a brake pulsation that “keeps pulsating even after I let off the brakes.” That sounded kind of anomalous, but that’s how I wrote it up. She left it with us, and later that morning I grabbed one of my guys and we launched our diagnosis.
The first thing I noticed as we started it in the service bay was a really high idle. As a matter of fact, the idle was so high I wondered if the foot feed was fouled by a wrinkled up floor mat (I’ve seen that more than once). I sent my guy to fetch a scan tool, and we retrieved the DTCs and found only a P0455 – no surprise on one of these – and then proceeded to hack into the live data, where we noticed right away that the reported throttle position sensor voltage was a lot higher than the baseline minimum. That would explain the high idle.
When the PCM wakes up on most platforms, it pegs the TPS voltage at key on and tags that number as the baseline for closed throttle. On some platforms, that number is stored as a part of the adaptive memory. But on the ones that re-read it at every key on, any voltage higher than the baseline after initial start is considered part throttle for the rest of that drive cycle, and at part throttle, the IAC steps will be high, poised for dashpot function (slow return to idle so as not to stall). As long as the TPS is considered to be at part throttle, the IAC will remain that way, which makes for a fast idle on non-electronic throttle body systems, even with the throttle plate closed.
After a moment or two, and a tap on the throttle (which is almost reflexive when the idle is high like this), the idle more or less normalized, and we backed out of the shop. When we had cleared the runway, wheels up and locked, we reached cruising speed on the four lane and slowed at the first turnaround to feel the brakes. We didn’t feel a brake pulsation, but we did feel the engine laboring as the vehicle slowed – the transmission was in high gear and continued to quiver and labor – even after we let off the brake – before dropping back into low gear when we were almost stopped.
I had felt this kind of thing before on other vehicles – GM platforms, mostly – when the TCC solenoid was sticking and keeping the converter locked while the vehicle was coming to a stop. In one of those cases we did a transmission service and dumped some Sea Foam trans tune in there – and fixed that one. In another case, we did the same thing to a 2008 Impala that was reportedly having screwball transmission issues and it fixed that one too. Sometimes the quick and easy is the smart way. Sometimes the quick way is the only way when there isn’t time for anything else.
In this case, with the TPS reading like it was, I reasoned that the controller might be confused enough by the faux part throttle reading to delay the downshifts, and so we sold the Jeep driver on the notion of planting a new TPS on the throttle body just to see what happened – I was convinced that it needed that anyway, and it’d be an easy beginning.
Not so easy
We obtained a replacement part from the parts store and my guy set about to remove the old one and install the new one. Well, he tried to remove the old one, anyway. He got the top screw out but couldn’t move the bottom one. We all know these screws have thread locker on them and can be tough sometimes. GM Instructor Ellen Smith mentioned this annoyance in the CCC school I attended in 1981, suggesting the use of a soldering iron on the stubborn ones. We initially tried that strategy, but this one was ridiculously tough and destroyed two Torx bits, so we removed the throttle body and carefully mounted it in a vise. Nothing would move it, not even a good pair of Vise Grips. Sometimes even the easiest job can turn into a “monsta,” and this was an extremely defiant little fastener. We heated the boss with a bottle torch and continued to tighten the Vise Grips to the sides of that domed screw head, but it still wouldn’t turn. We then ground the head off with an abrasive cutter and removed the sensor to expose the screw shaft in hopes of getting a better grip, but it still wouldn’t move – it was one with the throttle body. This was getting stupid.
Finally, I put away the bottle torch and hit the boss with a heat gun on high for about two minutes while applying Herculean pressure with the Vise Grips, and the shaft of that terribly stubborn screw finally began to turn. It amazed me to no end that the heat gun did what a blue flame wouldn’t.
With the new TP sensor installed and the throttle body re-mounted, we re-drove the car, didn’t feel anything untoward, and turned it back over to the driver. A week later she came back in for an alignment and reported that her perceived “brake pulsation” was gone. In a word, what she misidentified as a brake pulsation, we identified as an extremely late downshift, and our decision to treat the high idle/TPS problem turned out to be a surgical repair, and it felt good to get this one right the first time. And while we sometimes stumble around looking for the right fix, sensible decisions and surgical repairs are the benchmark of a true professional, but in our better moments, we all know there is no such thing as a 100 percent guarantee. This Jeep transmission fault may yet darken our door again.
