by Steve Bodofsky
© Steve Bodofsky
All rights Reserved
Used by permission
It makes you wonder if anyone ever really follows proper procedures. And, if not, how did they become "proper" procedures in the first place?
Actually, the answer is very logical: Procedures become considered proper by keeping the technician on a repair path that solves the problem efficiently, without expending more time or effort than necessary, and by preventing him or her from performing unnecessary tests or repairs. If you find yourself chasing ghosts or throwing parts at a problem instead of closing in on it, chances are you've skipped a step in the procedure
Of course, there are plenty of case histories to prove that bypassing the procedure can cost time and money. The pages of GEARS are littered with those tales of woe. But what about a shop that does follow procedures? How do those stories play out?
It might surprise you to learn that there are no marching bands... no fanfare to indicate the difference. Oh, sure, the shop owner may have a little more hair, and he may smile a bit more easily. And the techs may drive a little flashier cars, or their boats may be a few feet longer. And of course, they probably have a bit more time to spend on them. Nothing that'll really jump out at you. '
But there is a difference. In this issue, we're going to follow a car through a shop that does follow proper procedures, to see how the situation plays out. And then maybe we'll see how things might have been different had they not been so careful to follow proper procedures.
The car was a 2000 Buick Century, with a v-6 engine and a 4T65E trans. The customer was an older gentleman, who's maybe just a bit less observant and articulate than you might like.
He drove the car to the shop, and his initial explanation was something about a "banging." Further questioning had him reaching for his neck, talking about how it was snapping back. Rather than press further, the service writer smiled and suggested: "Why don't we go for a drive, so you can show me the problem?"
During the road test, the situation became obvious. The shifts were harsh…. harsh enough to snap your neck back at times. "You see how it is?" the customer asked. There was no question what he was complaining about.
At the same time, the service writer noticed, the Malfunction Indicator Lamp (MIL) was lit. "Has that light been on since the problem Showed up?" he asked. The customer said it was, but he didn't sound all that sure of himself.
So they returned to the shop, and the service writer wrote up a repair order, mentioning the harsh shifts and the MIL. Then, to cap it off, he attached a sticky note with the words "See Me First" on it.
Upon receiving the repair order, the technician saw the sticky note, and went to speak with the service writer. The service writer explained what he found, and what the customer had to say about it. Now the technician had all the information available, and the ball was in his court.
The technician walked out to the car carrying a scan tool. Even before he started the engine, he connected the scanner to the Diagnostic Link Connector (DLC) and checked for, codes.
Code P0748 was in memory: An electrical problem in the Pressure Control Solenoid (PCS) circuit. The technician recorded the code on the repair order, and then cleared it from memory. Now lie was ready to road test the car.
The code returned almost immediately after he started the engine. During the road test the shifts were harsh, just as the service writer had indicated. A quick check of the sensor signals didn't reveal any other problems.
Since the code indicated an electrical failure in the Pressure Control Solenoid circuit, the tech switched the scan tool to examine the PCS data. Scan data provides three parameters for this circuit:
PCS(%) - the duty cycle command from the computer to control the
current level through the PCS circuit
PCS DES (AMP) - the current level you should expect to see going
through the PCS circuit, based on the system voltage and the duty cycle
command.
PCS ACT(AMP) - the actual current flow through the circuit.
During normal throttle levels, the PCS(% ) should be around 25% to 30 % it stayed pretty close. The PCS DES(AMP) should be between 0.90 amps and 1.1 amps; give or take. It was.
Next, he switched to PCS ACT (AMP), to compare the actual amperage to the desired amperage; the two should always be within 0.16 amps of each other. Not this time: The actual amperage was zero. That means there was no current flow through the circuit - well that explains the code and the harsh shifts!
So here's what the tech knew so far: The computer was developing the correct command signal based on load, but it wasn't seeing any current through the circuit. Time to get the car back to the shop, and start digging a bit deeper.
Back at the shop, the first thing the technician did was to open the hood and just look around for any loose wires or obvious problems. No luck. Next he checked for any bulletins on this specific situation. Nothing showed up on the computer or in his ATRA bulletin package.
Now he was ready to begin his diagnosis in earnest. The code indicated an electrical problem in the PCS circuit and the scan data confirmed that. So his first step was to check the PCS circuit. With the key on, engine off, he back-probed the connector terminals for the PCS solenoid on the transaxle connector, one at a time. The ground signal seemed okay, but there was no power to the positive terminal (red/black wire). Ah-hah! That's why there was no current flow through the circuit.
The next step was to check a wiring schematic to see where the power for the PCS solenoid was supposed to come from. The schematic showed the computer-supplied power through terminal 45 (red/black wire). He back-probed terminal 45 at the computer connector and found system voltage.
Okay, there was voltage from the computer, but not at the trans axle connector. The obvious conclusion would be that there was a break in the wiring, somewhere between the computer and the transaxle connector.
Before going any further, the technician decided to make sure the solenoid itself was okay - no sense diagnosing half the system without making sure the rest of the circuit was all right. First he turned the key off, disconnected the trans axle connector, and then used an ohmmeter to check the solenoid resistance. It was about 4.3 ohms; well within specs.
Next, he reconnected he transaxle connector, and ran a jumper from computer terminal 45 to the solenoid power feed at the transaxle connector. Then he cleared the code again, and went for another road test. This time the transaxle worked perfectly; the PCS ACT(AMP) was back to normal and the code didn't return.
That confirmed it: The solenoid itself was fine. The only problem had to be a break in the wire between the computer and the transaxle.
Now the technician had two choices: He could run a new wire directly from the computer, or he could see if he could find the break in the wire. He started by checking to see if the break was reasonably accessible, by opening the conduit near the transaxle.
And there it was, about a foot or so away from the transaxle connector, right by the A/C bracket: The harness had been rubbing against the bracket. It wore through the conduit, and caused a break in the PCS feed wire. A simple repair... a slight relocation of the harness... and the car was good as new.
By following proper procedures, the problem was identified, isolated and repaired without wasting time or money. The whole job took about an hour. The technician was free to get onto another job, and the customer was thrilled when he got the bill.
Of course, not every shop follows "proper procedures." In all too many shops, a code P0748 would have been all the technician needed to see. He'd have ordered a new PCS solenoid and replaced it. After all, why waste a lot of time with additional diagnosis?
But as we've said more times than I care to remember, a code doesn't necessarily mean the component s bad. It just indicates a problem in the circuit. If you don't check the circuit, you're likely to get burnt.
And replacing the PCS solenoid is easier said than done: To reach it, you have to pull the side cover. On the 4T65E, it's almost easier to remove the transaxle from the car than to pull the cover.
What's more, after nearly 6 hours of labor, that shop would have been no further along than before it started: The problem would still be there, but now they'd be into the job for 6 hours plus the price of the solenoid. The only thing they'd have learned from all that time and money is that the solenoid probably wasn't bad after all.
Then, even if they found the actual problem without too much hassle, they'd have two choices: Eat the wasted labor and lose money on the job, or charge the customer for a lot of unnecessary work and a solenoid he didn't need. Either way, somebody was going to be unhappy.
So you be the judge: Does it pay to follow proper procedures. .. Or not?