The vehicle is a 2012 GMC Acadia with a 6T70 that has 85,000 miles on it. It comes to us from a dealer, and it belongs to a dealer employee’s relative. What difference does who owns it make? Bear with me, it all comes together to create a nightmare.
The vehicle was a 2006 Pontiac G6 with a 2.4-liter engine and a 4T40-E transaxle. The customer complained that it was shifting hard all the time. OK, let’s take a survey: How many of you have your hand up saying, “I want that job; bring it on?” My thoughts when I saw the repair order with that complaint were that it should be a fast fix and easy to troubleshoot. Oh, boy, was I wrong.
Here is a trouble vehicle – a 1999 Chevrolet 4WD Silverado extended-cab pickup – suffering from a problem whose unique cause was difficult for us to find. The customer’s complaint was that the transmission-to-transfer-case adapter had cracked repeatedly. I don’t know the exact count, but by the time we were blessed with this job I think the count was three broken adapters. Figure 1 is an example of one of the broken adapters that was cracked near the transfer-case mounting bolts.
Knowing about specific transmission problems still doesn’t stop folks from asking whether it’s OK to keep driving their vehicle. A customer has a 4L60-E transmission that has no reverse, second or fourth and he wants to know whether he can drive it to work this week or would it last until his next payday. Another customer has a 4T65-E with a P1811 code and wants to know whether they can make a trip over the weekend, or yet another customer who has a 5R55E with a broken third-gear band wants to know whether it is safe to drive.
After the customer left, I hopped into the vehicle and pulled it up in a bay, noticing that the speedo cluster’s odometer was not lit up, nor was the speedo working. I grabbed a scan tool, and, sure enough, it had a 452 code for loss of speedo signal. I thought blown fuse, because the odometer was not working. I checked the fuse and it was blown.
Now isn’t this an odd title for an article? Is the title insinuating that the transmission and the cooler line are competing with one another? I thought transmissions and cooler lines worked together in harmony. Well, I know at our shop, we have certain cooler lines that have drawn special attention in the past couple of years. We have been ‘clipped’ with some unexpected comebacks.
About 30 minutes later I got a call from the wrecker driver and he asked to talk to me. “This is scary; now what went wrong?” I was thinking. The wrecker driver told me he was “stumped.” He explained to me that the vehicle was in a position where he couldn’t get it loaded. Then he explained that the truck wouldn’t roll, as it was hung up – you got it, on a STUMP (see figures 1 and 2)!
With the transmission industry changing almost every day, we have to stay on top of the “3 C’s” if we plan to survive. The 3 C’s, of course, are Complaint, Cause and Correction. But in the transmission business, working through the 3 C’s can leave us a little short of our goal. We can’t quit just because we have found a bad part. Once we understand that a particular part has failed, it may help us to reduce repeat failures if we can understand why it failed.
With a basic understanding of TAPS, the Transmission Adaptive Pressure System, covered in last month’s article, we will now try to tap into the Steady State Adapt System and what its data can tell us. Not all scan tools provide steady-state data, but I’m convinced that this information is a real help in diagnosing problems in the later GM units. Data for the examples I used in these articles was recorded on either my GM Tech2 or my Mastertech. All the units in the examples shown below are 4T65-Es.
TAPS is one of the latest acronyms to join the list. It stands for transmission adaptive pressure systems, and it is used both for shift adapts, which establish pressure control during the shift, and for steady-state pressure control, the adapting-pressure requirements for a given gear after the shift is completed.
Here’s a real-life example of a problem that came into our shop. A 1998 Chevrolet pickup with a 4L60-E was brought in with complaints of no reverse, no 2nd and no 4th gear. We figured this was a routine job. In fact, it’s usually a “gravy” job. We started the job by scanning for codes and found P1870 and P0300.
Occasionally, we find the problem to lie outside the transmission/transaxle, in such parts as the MLPS (manual-lever position sensor), TPS (throttle-position sensor) or MAP (manifold-air-pressure) sensor, to name a few. Though it’s rare, even the computers/modules (such as the vehicle control module (VCM), transmission control module (TCM), powertrain control module (PCM) or engine control module (ECM)) fail from time to time. We have become accustomed to troubleshooting these systems, and although they are becoming somewhat routine, we all know that we run into some problems that “push” you. They either push you into being a better technician or push you closer to finding a different occupation.