Communication, Communication, Communication
Every now and then I get a job in with a serious communication barrier. This time it was a 97’ Chevy 1500 K series. No start or communication with PCM.
Should've been an easy in-and-out job, or at least that’s what I thought it was going to be. The truck was from one of the many Spanish-speaking shops that use my services. I don’t speak a lot of Spanish (wish I knew more), but the guys at this shop know I’ll be patient with the language barrier, and somehow communicate what needs to be done.
It all started with a rebuilt transmission they installed. After it was installed they had a service bulletin to do; which required moving a couple of wires on the PCM. The directions they had were very clear, in fact, it had detailed photos along with the instructions to make the update. They tried to do it, only to find out one of the wires didn’t match the drawings. (There was a year difference between the directions and the actual year of the truck.) Instead of going any farther, they sent me the truck to see if I could help them out. When the PCM was plugged back in with all the wires back in their connectors, the truck wouldn’t start anymore. Now, instead of driving it over, they had to tow it.
The truck showed up the next day, not a pretty sight to say the least. It had over 250,000 miles on the odometer, with a lot of bent and twisted body parts. The driver’s door was sagging to the point it would catch the fender every time you opened the door. Not exactly a fine ride, but as a work truck … it’ll do.
You know, it’s not that “Murphy” hangs around my shop, but he sure wanted me to earn my keep on this one. Some day I’m going to have a little “communication” with Murphy himself. He really knows how to make things tougher than they need to be.
I hooked up the scanner to see what was going on. Although it had perfect communication with the ABS, the Airbag system, it could not connect to the PCM. My first thoughts were the wires were not back in correctly, or one had pulled out when they re-connected the computer. That’s where the fun began. Every single wire was not only in the correct spots, but all the powers and grounds were there. I’ve seen these problems before, and it almost always turns out to be a corrupted, or lost, data line. Now of course, there are a few other possibilities, but the data line is usually where I try first.
My method of checking for this is kind of problem is to isolate the data line between the computer and the ALDL 16 pin connector. Then run a bypass line from the PCM directly to the ALDL, and check the data line again. This time that didn’t work… still nothing. Now things are getting a little serious. Time to check it with the scope. After verifying the voltages and ground signals (again) with the scope; I looked for a scope reading for the actual data line. Oh, oh… flat line, it’s a bad PCM. I haven’t a clue what they could have done to the computer from just changing a wire or two, but it sure was dead. I called the shop owner to let him know.
“I’ll bring another one tomorrow morning,” he tells me in his broken English.
The next day a “salvage” computer was dropped off at my shop. Without hesitation I popped it into the truck, turned the key on, and ran it through security setup. (Thinking I’m done, and there wasn’t any reason to check any farther.) But, it still wouldn’t start. Ok, what’s the deal? Did I miss something? Now I’ll have to re-check everything I just did yesterday, again. I checked the powers and grounds, and all the other wires and connections this time. But there still wasn’t any communication with the computer. Could it be another bad PCM? It sure seemed that way. I’ll have to call the shop owner and let him know what I found out. This time he decided to go to one of the discount parts stores, (where he gets his parts from), and pick one up.
Third computer and another failed attempt at communication. Not that I wanted to spend the rest of the day doing all these tests over, but there had to be something I was missing or a really good reason for this catastrophe. Before calling the shop owner I wanted to make absolutely sure there were no mistakes in my results. I happened to have an extra set of connectors off an old harness from a car I salvaged out, which I made into bench test plugs.
The connectors are clearly marked with the color and the numbered connection pins. To get the PCM to talk on the bench, all I needed were the correct positive and ground leads and of course that very important data line installed into the test plugs. This way, I could bench test the PCM without interfering with the wiring in the truck. A simple scope reading could tell me what was going on. No communication should be a thing of the past now.
I wasn’t a bit surprised… the weirdness continued. This PCM doesn’t even turn on, completely dead. I re-checked my pin positions several times, I was absolutely sure I had them right. It can only mean one thing… another bad computer.
Would you believe this went on for two more times? Each time the owner would exchange the computer, I would check it with my little bench plug set up. Each time it did the same thing. I couldn’t be sure but there’s a pretty good chance his broken English wasn't communicating his needs to the parts store either. I thought I'd be a little sneaky on the next exchange. I secretly installed some clear tape on one of the connectors. When the shop owner returned with the next "exchanged" computer I knew what was going on. He was handed the same computer over and over and over again. My tape was still over the terminals.
Finally on the 5th or was it 6th try I got what I wanted… COMMUNICATION! WHOO HOO!
I can’t remember a job that I went over the same test procedures so many times and still couldn't get results. There’s that old saying; “Doing the same thing over and over again and expecting different results is the definition of crazy.” Oh yea, I was totally feeling the “crazy”. It sure applied to this job.
There was a point where I started doubting myself, but I stuck to the test results and double-checked my work each and every time to make sure I had it right. Even though the shop owner was getting concerned that I may never solve his problem; he made the commitment to see it through.
Even though we had a language barrier between the two of us, (and the parts store) the communication with the PCM was just as much a barrier, that PCM couldn’t understand either Spanish or English. All I wanted was any form of communication.
In every different direction there was a communication problem. From the shop owner, the part store and that bad computer that kept coming back. Job solved, customer is happy, and I'm sure glad of that. Well, I may only speak a little Spanish, but I can speak a little computer. I guess that makes me a little bilingual too.
