P0172 System Rich

[Trans Man]

I have a 99 SL2 with code P0172. I had removed the computer and replaced it with a SOHC computer, but still have the old one DOHC. Originally my mechanic said the computer wa no good, so I istalled a used one but later found out it was a SOHC not DOHC. If I put the DOHC back into the car will it help resolve this code issue?
What is the easiest way to fix this code so I can pass inspection.
Any help would be appreciated

[jss21382]

Did it have the code before you change the computer? The most common things I see causing p0172's are biased upstream o2 sensors and biased map sensors, which is where the ecm get's it's barometric pressure reading that is uses as a modifier to the fuel map. So if it it's reading the wrong barometric pressure (below sea level ususally) it'll increase the fuel map to a point where it sets a rich fuel trim code.

[madpogue]

Visit our How-To Library and search on "ECTS". It's a temp sensor that's prone to failure, and is an exceedingly common contributor to our cars running rich.

[Trans Man]

Not sure if the P0172 showed with the original computer installed.
My mechanic had indicated that he thought it was the computer and it would cost $1,200. I decided to purchase a used one and install it myself.

[OldNuc]

Originally Posted by Trans Man

I have a 99 SL2 with code P0172. I had removed the computer and replaced it with a SOHC computer, but still have the old one DOHC. Originally my mechanic said the computer wa no good, so I istalled a used one but later found out it was a SOHC not DOHC. If I put the DOHC back into the car will it help resolve this code issue?
What is the easiest way to fix this code so I can pass inspection.
Any help would be appreciated

Replace the DOHC computer before you burn the valves out of the engine. Then read the thread below and do not start throwing parts at the car, all you will do is spend lots of money. Its not the O2 sensor, in most cases with these cars.

Get some of your favorite beverage and read through this thread.
http://www.saturnfans.com/forums/sho...d.php?t=128804

Then information is needed.
Have you changed the plugs and wires? NGK BKR5ESA-11 plugs only
Replaced ECTS?
Has the fuel filter/regulator ever been changed?
What other maintenance has been done to the engine?
How many miles?

From the UHJB remove the PCM I and PCM B fuse and replace the DOHC computer. Replace the fuses. Now start car and see when the SES comes on, accelerating, or cruise, or decelerating, or idle.

This is not caused by the computer, its not broke.

You can get he codes read at almost any parts store. We will need the number of the code and not someones interpretation as to what they think is broke.

[adventureoflink]

Originally Posted by Trans Man

Not sure if the P0172 showed with the original computer installed.
My mechanic had indicated that he thought it was the computer and it would cost $1,200. I decided to purchase a used one and install it myself.

RUN, don't walk, from that mechanic. PCM failures in general are one in a million.

http://www.obd-codes.com/p0172

[OldNuc]

There is no MAF on a Saturn.

[adventureoflink]

Originally Posted by OldNuc

There is no MAF on a Saturn.

I never said there was. I link to obd-codes to get an idea on how to troubleshoot the problem, although FWIW I remember someone made a long P0172 thread and it ended up being their timing mechanisms

[OldNuc]

The p172 can be either mechanical, which is rare, or one of 4 other items which are sensor or component related.
This is the actual code description that pertains to Saturn. The ones at that web site are generic GM. Saturn is not GM....

This will be a bit hard to read as the photo section is down and the file attachment limit is a bit restrictive.

The Saturn code definitions and trouble trees are not on the Internet anywhere free.

[cboss]

I agree with OldNuc.

Put the old computer back in.

Also when you do, buy some electronics contact cleaner (in a spray can. Get CRC brand) and clean the computers contacts as well as the wiring connectors to the computer.

Also there are two (at least on my 96 SL2) grounds on the engine. One in front above the coils and the other below the intake manifold near the #4 cylinder. Remove the nuts, clean the stud the bolt goes to, the wire connectors and reconnect the grounds. A poor ground will effect the computer. The ground under the intake manifold is a pain to get to, but it can be done.

The next question is:

Why did the mechanic say the computer was bad ?
He should have explained carefully and in detail "why", since the computer is expensive to replace and he better have a good reason to replace it.

My gut feeling is that 'some" mechanics have a poor understanding of how the engine computer system really works and it is easier to just say the computer is bad, than to know how to diagnose the problem.

Engine computers are quite complex and there are many factors that can cause problems for the system (ie. sensors, wiring, mechanical problems).

I spent a good 6 months or so trying to track down the cause of the P0172 code in my car. Sadly mine was a mechanical problem.

From what I have read, it is rare for the computer to go bad. They have to be built tough to last and they are.

When diagnosing something like the P0172 code, one needs to carefully examine the OBD-II data from a computer scanner. Also there are a number of physical causes as well (ie. vacuum leaks, bad fuel injectors, bad fuel pressure regulator).

Once you get the old computer back, pull the spark plugs and clean them (or replace if necessary), so you know you have a good spark. Its a good precaution before tracking down the P0172 code.

Clear the codes, drive the car for awhile and see if the code comes back.

Document on the forum any symptoms (no matter how small) of any problems, even if the code does not come back. Then you can examine the symptoms one by one and start diagnosing the problem.

Rule of thumb:

Diagnose before replacing parts.

There are a number of diagnostic tools, that even the DIY'er can learn to use which should be the first step, such as:

- Compression gauge
- Fuel Pressure gauge
- vacuum gauge
- OBD-II Scanner which reads "live data"

For diagnosing P0172, the Fuel Pressure test is important. Then a vacuum test can tell you the overall condition of the engine mechanically. If neither of those tell you anything valuable (meaning no problems), then next is the OBD-II scanner and check the MAP (air pressure) sensor, ECTS (coolant temp), AIT (intake air temp), O2 (oxygen sensor), RPM at idle, fuel trims.

Also a good scanner can read what is called a "Freeze Frame". It records all the live data at the moment the code was triggered. This is helpful because it gives a clue of when the code gets triggered (ie. is it at idle, a high speed, etc.).

The P0172 code is one of the most difficult to track down and can get costly if one pays mechanics, especially if they are not good at diagnosing computer problems (most are not IMO). I would venture to say that it is a minority of mechanics who fully grasp the proper diagnosing steps in such situations. The small price for a decent OBD-II scanner could save you hundreds of wasted dollars later. If money is tight, then maybe you could rent for a day a fuel pressure guage from the autoparts store and then purchase an OBD-II scanner and a vacuum gauge (the poors mechanics best friend). Those two tools alone may lead you in the right direction.

[OldNuc]

+1^^^I would agree. This requires a plan.


adventureoflink; I have to ask, what is your avatar representing?

[adventureoflink]

Originally Posted by OldNuc

adventureoflink; I have to ask, what is your avatar representing?

Hahahahaha. glad someone took notice

anyway, it's a Mr. Saturn. http://en.wikipedia.org/wiki/Mr._Saturn#Mr._Saturn

Since this IS a SATURN forum.. figured why not?

[OldNuc]

I figured it was a game piece from somewhere. Been meaning to ask for the longest time.

It is different.

[adventureoflink]

Originally Posted by OldNuc

I figured it was a game piece from somewhere. Been meaning to ask for the longest time.

It is different.

A different kind of game piece, indeed. Heck, in Earthbound and Mother 3 it even has its own font!

[OldNuc]

I did notice that this one came with a new alphabet and script.

[adventureoflink]

Originally Posted by OldNuc

I did notice that this one came with a new alphabet and script.

It does. It's even known for saying things out of random, like ding, zoom, boing, kay-o, and Dakota...

[OldNuc]

Dakota sounds serious....

[adventureoflink]

Originally Posted by OldNuc

Dakota sounds serious....

INTERNET SERIOUS BUSINESS LOL

but yeah, how's your code doing Trans Man?