So many codes back to back

DIANA SMITH4

MEMBER
2009 VOLVO S80
6 CYL
AUTOMATIC
117,500 MILES

Hi,

I bought the vehicle listed above s80 3.2 with almost 110,000 miles on it. It had been neglected, and the friend I bought it from assured me it was a good car. I have had it for almost two years. The 2nd week after I owned the car some non-mechanical things fell off or stopping working, but that is when I got my first check engine light.

I brought it to the same garage that had fixed the other issues, and the first "fix" cost around $1,800.00. The check engine light came back on within a day. Brought back, another, a different set of codes. Replaced, drive home, light comes on. This happened 4 times, every time the light came back on as I was driving from mechanics. The last time, actually, the mechanic was taking it for a test drive after fixing it, and it came on.

Fast forward it's almost two years now and the light has never gone off, but the car seems to runs pretty well. The mechanic had said the engine needed to be reset, but no mechanical problems. Well, not true. My emissions test is coming up, so I brought into the shop [different mechanic] for a "once over" to tell me what needed to be fixed. 4 codes came up all centered around the heating element? They replaced one sensor and did a little bit of other stuff. Check engine off! Yeah. Mechanic drove tested it, check engine back on. I ran an OBII scan, 4 new lights, and 2 old ones.

So, my question is this, if all these codes indicate something wrong, why do they come up like they do, right after the car is fixed or parts are replaced? I can't believe it's not related since 5 times now, the codes were addressed and replaced, the light went off, and within a couple of miles came back on 5 times. How can something be wrong each time right after? Why wouldn't the codes come up all at once if all these things were wrong. I feel as if it will never end because it hasn't. Now I have put more than $4,000.00 of repairs into this car, and it is going to keep going. Do you want to guess how many miles I have put on in less than 2 years? Nine thousand. 9,000 in two years! So I have basically been fixed the things prior owner neglected, and maintenance for myself. Is this a situation where you never fix the car but have new codes all the time? Thank you so much. I feel like I am going insane.

4 Replies

MASTER ASE TECH

MEMBER
82 POSTS

Hi, My name is Dan.

A lot of codes will not set on the first key cycle. Meaning the car has to be driven, the computer sees an issue, but then wont turn on the light until it sees the same issue happen again. I've attached a couple articles about codes.
You may want to purchase an inexpensive code scanner (about $35.00 to $40.00)so that you can read the codes and reset them yourself.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

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Friday, August 27th, 2021 AT 11:13 AM

STEVE W.

MECHANIC
13,572 POSTS

To add a bit to Dan's post, another item is that you can have a code set such as the heater code you mentioned that will prevent other tests from running while it is set. Then once that part is repaired or replaced the tests run and now the other issues that were hidden by the failure of those tests to run show up. I suspect that the new codes are related to the catalytic converter(s) as the O2 sensor codes you had would have prevented those tests from running. That is one of the reasons I tell people not to drive around with the light on, it can hide a worse problem. I second Dan's idea of getting a code reader and reading the codes yourself, you could then post them here and get an idea of what the problem is and what the repair would be.

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Friday, August 27th, 2021 AT 3:23 PM

DIANA SMITH4

MEMBER
2 POSTS

Seriously though, it seems bringing your car to a shop is not a simple matter, but it seems almost as if you have to interview the mechanic as to what way he diagnoses and repairs caused. Joe do you just use the scanner do you find the problem is so complicated?

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Sunday, August 29th, 2021 AT 7:00 PM

STEVE W.

MECHANIC
13,572 POSTS

Modern cars are very complex. To give you an idea the attached image is of the modules on your car that can cause codes to appear. Not all of those codes can cause other tests to stop but many can. For instance say that you were to step on the brakes. That simple step activates control and monitor circuits in 10 different modules. Two of those modules do nothing but activate the left and right brake lights!
Most shops will tell you if a repair of a system may let tests run that could then trigger other codes, but it might be overlooked.
Newer cars are even worse with the amount of computers and modules in them with some European brands having over 100 modules in the system. The thing is that a scan tool depends a lot on the abilities of the person to diagnose the issue as none of the codes actually says this is the bad part, replace it. Instead the code indicates something the computer sees as wrong. To put it in different terms, Say you are out walking and step down and feel a very sharp pain in your foot. Your brain says "Pain in foot" but it doesn't say, the pain is from the nail you just stepped on, or the stone that got into the shoe, or the rock you just stubbed tour foot on. It just sees pain. Then you have to look for the cause. No different with codes.
A P0301 for example, it says you have a misfire on cylinder 1. It doesn't say that the code is from a bad spark plug, a bad coil or an internal engine problem. However that code will prevent an O2 sensor test from running. So you repair the faulty injector, then the O2 test runs and the excess fuel from the injector has damaged the upstream sensor, so that now sets a code. Then you repair that and now the full test runs and another code, a P0420 is set which means the converter was also damaged by the excess fuel. But due to the first code blocking the later tests you won't find that until all the tests have completed. And that is a simple code.

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