12 GEARS August 2008

When we recently invested in a new laptop-based scan tool, we received J2534

reflashing equipment with it, and start-ed doing reflashing. Overall it’s been an interesting endeavor. Here are three interesting situations I’ve encountered.

Customer Folly – 1996 1-Ton Chevy Truck 5.7L with 4L80E

The truck came in with high gear starts every time, and a code P1886 for the 3-2 solenoid circuit. The code would reset every time you started the engine. I started scratching my bald head; if memory served, only a 4L60E has a 3-2 solenoid. Some quick research confirmed my memory.

I thought maybe it was a problem with our new laptop-based scan tool. But our old reliable handheld scan tool revealed the same code.

A quick look at the VCM showed the salvage yard markings (figure 1) that tell the tale. The customer had put in a boneyard VCM. Was it the right one?

I reconnected the new scan tool and pulled the VIN from the computer. It didn’t match the truck. Running the VIN through a VIN decoder showed the computer came from a 5.0L ½-ton truck with a 4L60E. It’s gotta be the wrong computer, right?

Then a thought popped into my mind: What if I treat this as a new com-puter and initialize it (install the software on it) to match the VIN for the truck? So far I hadn’t used the J2534 equipment (figure 2) to initialize any computers; only to reflash the current software to newer versions. So I tried it.

Ten minutes later the vehicle was reprogrammed and the VCM output a VIN number that matched the truck. The code didn’t reset, and a test drive confirmed that the truck was fixed. Total time spent? Less than 45 min-utes.

So was the VCM wrong? Absolutely not. This computer fits a wide range of vehicles and engines. The same computer could be on an S10, Astro, ½-ton, 1-ton, Tahoe, etc. It could also be matched with a 4.3L, 5.0L, or 5.7L engine. The only difference is the software. So even though the number was correct, you can’t just order a VCM from a salvage yard and slap it in. If you do, insist that it come off an exact match vehicle.

Naturally, the customer never told us that he’d replaced the VCM, or that the problem began when the VCM was replaced. He insisted it started 3-4 days later.

That Annoying Little Light – 2001 Saturn

This car came in from a nearby shop with the engine stalling. They claimed there was a bulletin about a reflash to fix the stalling, and wanted us to reflash it for them. I couldn’t find the bulletin but there was a reflash available for the car so we tried it. It did seem to fix the stalling problem, but after we finished we had a P1336 code (CASE learn error). The car would run and drive, but that annoying “Service” light would come on every time you started the engine.

Now a little background: During my first GM reflash, I received a mes-sage saying “You MAY need to perform Crank Angle Relearn with the TECH II.” I don’t have a Tech II, but I hoped one of my scan tools could do the job. I gotta say it worried me a bit though. I finished that reflash and tried to do the relearn with our scan tools: Neither

J2534 Reflashing J2534 Reflashing for Fun and Profit…

From the Trenchesby Richard Middleton,

Diagnostician for Peter Fink’s Certified Transmission in Grandview Missouri

Figure 1

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GEARS August 2008 13

J2534 Reflashing offered the relearn. Although it wor-ried me, I drove the car and everything seemed fine and no codes triggered, so I guess it doesn’t always need to be done.

By the time I got to this Saturn, I had quite a few GM reflashes under my belt. I’ve received that same mes-sage on every one, but up till this car, none of them needed the relearn. I also paid attention to whether my laptop-based scan tool had an option for the relearn: On some vehicles it did, others it didn’t.

So, when I reflashed this Saturn, I had done enough GM reflashes with-out a problem that I didn’t think twice when I saw, “You MAY need to perform Crank Angle Relearn.” Unfortunately this was one that needed the relearn. And neither of my scan tools was up to the job.

After a few hours of research, and finding no mention of Crank Angle Relearn procedure in Mitchell’s, I called friendly neighborhood shops that had a Tech II. They all told me there was a separate memory card for Saturns, and

all they had was the GM card. They may have been able to do the relearn with the GM card, but I’ll never know.

The tech helpline for my J2534 equipment told me there was a manual relearn for earlier Saturns, but no men-tion of the relearn for the year I was working on. We decided to try the manual relearn anyway. It’s easy to do:

Step 1: Let engine idle in park until the “Service” light flashes.

Step 2: Raise RPM to 3000-4000, until “Service” light goes out.

The “Service” light on this car is shaped like a little wrench. Step 1 took about 90 seconds, and step 2 took about another 20-30 seconds. And just like

Figure 2

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14 GEARS August 2008

that, the Crank Angle Relearn made that annoying little light go away.

Wake Up and Introduce Yourself – 2000 Caravan 3.8L with 604

Bruce brought his van back to us shortly after we installed a replacement transmission. While driving to a reli-gious retreat, some of the drivers fol-lowing him complained he was going too fast. Bruce explained that he’d been on cruise control at exactly the speed limit the whole time.

I’ve been around the block a few times and I know that a 3.3 unit bolted where a 3.8 unit goes will cause the speedometer to read slow, because of the differential ratio and transfer gear differences. Since this was a 3.8, I assumed this was the problem. The replacement unit may have accidentally been tagged with the part number for a 3.8, when it had the ratios for a 3.3.

I quickly pulled the transfer gear cover, expecting to find the wrong tooth count, but that wasn’t the case. Well then, it just had to be the wrong differ-ential ratio… but I was wrong and the ratio was right.

I checked pinion factor and it matched the tire sizes on the car. I’ve learned that substituting different tire sizes in the pinion factor doesn’t make any major difference to the speedom-eter output. This speedometer was off a significant amount. I tried substituting a few different tire sizes anyway, although I knew it was a waste of time.

At this point I didn’t know what to do. I just sat there, staring at my new laptop wishing that it could somehow magically make the speed-ometer correct. Although the thought seemed ridiculous, I knew of nothing else to do.

I checked for available reflash information for the ECM but there was none available. I thought this was pointless anyway because obviously the speedometer function is in the TCM, since the OSS inputs to the TCM, and

you set pinion factor in the TCM. Then I checked for available

reflashes for the TCM; there was one. It was in reference to bulletin 21-18-99 which instituted a change to ATF +4, which made it necessary for a “TCC Break-In” on NS/GS body vehicles. Bruce’s van was, of course, an NS vehi-cle. It seemed the only change to the software was to make the TCC Break-In function available on the TCM. Certainly though, this change couldn’t fix Bruce’s speedometer problem.

After working through the reflash, I checked the computer system: The van now had TCC Break-In. But did it fix the fast speedometer? Sure did! But why?

The TCM for the 604 fits a wide variety of vehicles and engines (sound familiar?). Although there are different part numbers, they aren’t necessarily engine specific. They’re definitely not differential ratio specific. If you check the TCM part number, it’s the same for a 3.3 and 3.8 in 2000.

So how does the TCM know wheth-er it’s controlling a trans with a 3.3 or a 3.8, so it can compensate for the dif-ferent ratios? Well, when a new TCM is plugged in for the first time, there’s a little “dialog” between the TCM and the ECM. The ECM shares information with the newly awakened TCM and the TCM stores this data permanently.

This only happens once, when the TCM is turned on for the first time. There seems to be no way to change

this. This little wake-up characteristic makes used TCMs undesirable because they aren’t customizable to your vehi-cle, making them unusable unless they are already an exact match. So why did the reflash fix it? A reflash is the one way to make the TCM wake up again.

Bruce never noticed any difference in the speedometer and he never said, “It wasn’t like that before.” I simply assumed it wasn’t like that before. The problem I had with reflashing the TCM was solved by reflashing it off-board, and when I removed the TCM to reflash it, there, under the TCM, where I couldn’t see it with the TCM bolted to the car, were the telltale salvage yard markings.

Bruce’s van had a used TCM, mak-ing his speedometer slow as long as he owned it. There aren’t many reflashes available for 604 TCMs, so in the off chance you run into something like this, don’t count on being able to fix it this way; you’ll probably need a new TCM.

Since equipping our shop for reflashing, we’ve discovered a number of fixes that never appeared in bulle-tins. It’s saved us from fighting through a futile diagnosis a number of times, and it’s why, when confronted with an unusual problem, one of our first con-siderations has become to check for a possible reflash. Today I don’t see how anyone can be in this business without reflash capability in house.

Figure 3

J2534 Reflashing for Fun and Profit… From the Trenches

Bruce never noticed any difference in the

speedometer and he never said, “It wasn’t like that

before.” I simply assumed it wasn’t like that before.

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1607-PRE-053 Gears Magazine April 2008, January 2008 T: 8.125 x 10.875 B: 8.375 x 11.125 4C

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