Wednesday, January 4, 2012
Code PO171 - GMC
Happy New Year!
As I exited my office on this, the first day back after New Year’s long weekend, a late model GMC Sierra drives in. Nice looking vehicle. The customer gets out - all smiles, and how are you, and how was your holiday. Nice guy, but I’d never seen him before. Since I have a nametag, it’s not uncommon for total strangers to be using my first name. I always take it at face value while politely conversing. My good buddy will be Joe Sierra. Joe’s a six footer, carrying about fifty pounds too much, thinning brown wispy hair, and a short goatee. I shake my best pal’s extended hand.
“I need you to give me a quick scan, and tell me what’s wrong.”
Now look. For my regular customers, I do indeed hook up my scanner for some quick code pulling. It’s like automotive triage so I know how much more time I’ll need to figure out what’s really wrong if it’s not obvious. I don’t do it for first timers, because most of the time the results are next to worthless, and they’re thinking oh boy, I’ll just replace that and everything will be fine. See ya! Then a few days later they’ll be in to blame me for telling them to fix the wrong thing, when I had done the exact opposite. I explain to Joe I’d be glad to check out his vehicle and how much it would cost for the diagnostic fee. I’m nearly half what the dealer charges. Joe loses his happy go lucky demeanor.
“I just need a quick scan, Bernie. I’ll bring it back in at the end of the week for repair.”
“It doesn’t work like that. Most of the time the code merely points to an area where the trouble lies.” I’m thinking it’s a new year. I have a few minutes. I’ll do a demo for a potential new customer. “I’ll show you what I mean.”
I bring out my scanner, enter the vehicle info (2006 GMC 1500 with 5.3L engine), and scan the truck. PO171 – bank one sensor lean. I’m thinking wow, you can’t ask for a better example than that. This code refers to the bank one cylinders’ monitoring air fuel sensor. It used to be called an oxygen sensor and gives information to the computer about the oxygen content exhausted by the bank one cylinders. It can get tricky like my out of town guest before Christmas with the Nissan.
I check the digital data and misfire readings. The fuel trims and sensor info are within spec’s. Then I check at what temp the code set. The computer decided something went wrong when the GMC was cold. I explain in detail to Joe how many things can cause the code that have nothing to do with the sensor, such as an electric fuel pump going out, a slight intake manifold vacuum leak, and even a slight exhaust manifold gasket leak when the vehicle is cold. Joe nods while watching me point out the normal readings on the scanner as if he understands.
“I get it. Give me your card, Bernie, and I’ll call you next week when I can leave it off with you.”
Good deal. I give him my card and he drives away. Tuesday, he’s back in, and Joe’s not smiling.
“I changed that bank one sensor and disconnected the battery to erase the code like you said, Bernie. The check engine light came back on and it ran real shaky for quite a while. Scan it and tell me if the same code set.”
Bingo! If the refrain in this story seems familiar to some of my friends… it is. I feel a lot like Dr. House on the TV show, only I don’t torture my patients before fixing them. :) Patients lie, patients deliberately mislead, and leave details out. They blame the Doc when he takes their input and they get worse, even though they gave him false data. It’s the same with vehicle repair, except with my large old time customer base I’ve built trust with over the decades. Strangers… not so much. Remember, I have to bring Joe back into reality, which I do quickly.
“Leave it now, Joe. I’ll find out what’s wrong and call you with an estimate. Come in the office and we’ll make up the invoice for the diagnostic check.”
“You’re going to charge me?”
“Yep. I’m the one who told you in detail how many things can cause that code other than the sensor and you changed it anyway. The reason it ran rougher is because you disconnected the battery and blanked all your computer settings to erase the code. That’s not a good idea for exactly the reason you discovered. Now, you’ll have to pay me to do the checks I would have to do normally to find out what’s wrong.”
Joe’s heart ain’t into taking this ploy any further. “Okay. Can I use your phone to call for a ride? I forgot my cell.”
“Sure. How long did it take for the check engine light to pop back on and what brand sensor did you use?”
“AC Delco, and the light blinked on pretty quick after I started it. It went off for a while, but when I restarted it yesterday afternoon after it had been sitting, it came back on and stayed on.”
“Okay, thanks.” I took his keys, and went about finishing what I already had in the shop. I decided not to get fancy because I had a good idea what might be happening. When I started the GMC cold with my scanner hooked up, I sprayed some quick dry brake clean stuff along the edges of the intake manifold. The oxygen sensor readings and fuel trim data started revving up and down along with the engine. As it warmed up the spray made little impact. That explained why he didn’t have a misfire code. I got Joe’s reluctant okay to replace the intake manifold gaskets and kept it until this morning after an extensive test drive late yesterday. It all checked out and Joe was even appreciative while paying the not inconsiderable bill. It’s around a five hour job. Another new year, but already a familiar story of intrigue in the Twilight Zone of auto repair where everything is my fault until proven otherwise, even freebies. :)
That’s all for this update from Nilson Brothers Garage, but if you’re appreciative of the information, here is a link to my new novel COLD BLOODED for Nook and Kindle. If you’re kind enough to read it and like it, please review it on the site you purchase it from. Thank You! Every little bit helps my writing gig. :)