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1998 Cadillac STS "Check Engine light"

Tiny
PATS37
  • MEMBER
  • 1998 CADILLAC STS
  • V8
  • FWD
  • AUTOMATIC
  • 44,302 MILES
1st of all many thanks to rasmataz & gstacey, Your information was spot on. However it only corrected half of the problem but it was by far the best information I got by any measure. I say half because the car is running fine in all respects except the check engine light comes on but none of the other symptoms before. Now there is no rough idle, no stalling, no loss of power on acceleration.

Now, the check engine light goes on, the car runs fine and after 2 or 3 starts it goes out leaving ths same 3 codes of 101, 171, 174.

Also I left out two other things the mechanics had done because they never charged me. They replaced the EGR valve and thoroughly cleaned the outer idle control motor.

I am hoping this additional information will further isolate the problem. There are no vacuum leaks. I am also making another donation because I truly believe that your continued help will eventually lead to a solution.

Pat
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Thursday, September 16th, 2010 AT 1:07 PM

12 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
Your getting a MAF code with 2 lean codes. That tells me that there is an issue with the MAF. Double check all the intake snorkels and attaching pipes. If you happen to be using an oil treated air filter, then just replace the MAF because it ruins them.
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Thursday, September 16th, 2010 AT 1:22 PM
Tiny
PATS37
  • MEMBER
  • 13 POSTS
Wrenchtech, thanks for the quick reply. The MAF sensor was replaced with a new OE MAF from a Caddy dealer about 5 Mos. Ago. (This is a year old problem.) The air filter is not treated with anything. They did clean it again just be sure, with a non oil MAF cleaner.

I know the MAF cleaner is not an "after market" unit as I picked it up from the dealer and paid for it. My question to you is, is there any way to check the MAF sensor to be sure it is good? Could it possibly be defective out of the box?

I am going back to them again tomorrow to double check "any pipes or snorkels" as you stated. If nothing wrong is found what would be your next step since I won't have access to my computer.

Pat
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Thursday, September 16th, 2010 AT 1:46 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
There is a whole series of tests to isolate the cause of the issue, assuming it's not an intermittent problem. You would need a scan tool for most of the testing.
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Thursday, September 16th, 2010 AT 1:49 PM
Tiny
PATS37
  • MEMBER
  • 13 POSTS
Wrenchtech, It is an intermitant problem as I originally stated. Now it comes on intermitantly and after a few starts it goes away still leaving the same three codes behind. The "scan tool" you speak of, is that the computer the mechanics use to read the codes? Or is it something else?

Pat
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Thursday, September 16th, 2010 AT 1:59 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
It's much more than a code reader. The professional versions can do a lot more testing than the cheap OBD2 code readers.
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Thursday, September 16th, 2010 AT 2:04 PM
Tiny
PATS37
  • MEMBER
  • 13 POSTS
Yesterdays replies from "wrenchtech" were not helpful at all. I donated $15.00 again before asking my question. Quite frankly an answer telling me what the problem isn't is useless. I took great pains to be very specific since my replies from gstacey and rasmataz earlier were quite specific.

I'm leaving in an hour to go back to my mechanics. If anyone there has anything useful let me know.I'm having my mechanics check the three wires going from the MAF to the computer and if they can't find anything then try to sheild them from any outside interference.

By the way, even I know enough that me or Cadillac would never use an oil soaked air filtter.

Pat
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Friday, September 17th, 2010 AT 9:25 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
No problem. I'll stop responding to you.
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Friday, September 17th, 2010 AT 9:37 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
I've ran across with the same codes on a Ford and it turns out to be the MAF sensor being the problem-While the engine is running tap on the MAF sensor and see if it stumbles, also might want to check the signal output of the sensor-

We appreciate your continued donation and we will continue to assist in this matter to resolve the problem. If you feel unsatisfied I ask you to request for refund
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Saturday, September 18th, 2010 AT 1:22 AM
Tiny
PATS37
  • MEMBER
  • 13 POSTS
Rasmataz,
This kind of info will be very helpful. As answered also by gstacey. The shop is closed for the weekend and I will be there Mon. AM

Thanks Pat
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Saturday, September 18th, 2010 AT 10:45 AM
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
Wrenchtech is right when he says the GM tech I scanner can aid greatly in this diagnostic, but here are things you can check:
1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK, then go to next step. 2. Using scan tool, check for stored DTC(s). If DTC P0106, P0108, P0112, P0113, P0300, P0401, P0441, P1108, P1404, P1406, P1441, P1508, P1509 or P1645 is also present, diagnose affected DTC(s) first. If DTCs are not present or after diagnosing affected DTC(s), go to next step. 3. Check vacuum leaks at MAF sensor seal, throttle body spacer, intake manifold, PCV, EGR valve, plate or tubes and brake booster and hoses. Repair as necessary and retest. If air leak is not found, go to next step. 4. Check for stuck or incorrect PCV valve. Check for air (unmetered) leaks at oil dipstick tube or oil filler cap. Repair as necessary and retest. If vacuum leak is not found, go to next step. 5. Using FREEZE FRAME and FAILURE RECORDS data function on scan tool, duplicate conditions under which DTC P0101 was set. If DTC resets, go to next step. If DTC does not reset, see DIAGNOSTIC AIDS. 6. Go to DTC P0106 and perform diagnostic test, then return to this step. If repairs were necessary, verify repairs and retest. If repairs were not necessary, go to next step. 7. Replace MAF sensor and retest.
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Friday, September 24th, 2010 AT 9:31 PM
Tiny
PATS37
  • MEMBER
  • 13 POSTS
To merlin2021, gstacey, rasmataz Thanks for all of the good information you gave me (gstacey wanted the Vin just in case there was a TSB covering this problem so here it is--1G6KY5496WU933672.

As far as a "help" web site, you guys are the BEST! After checking the entire system they couldn't think of anything (besides the MAF sensor) that could be wrong. So I took the car and did some driving, all sorts like up to 120 MPH from a dead start, and slowed the car down by down shifting back to low. No problem. So then drove in the city and did all sorts of things and no problem. On my way home the F@#$in check engine lite goes on again. This was on Saturday. However there were none of the other problems that plagued the car like stalling, rough and inconsistent idleing. So on monday I called and told them I was coming in. When I started the car the check engine lite didn't come on. The car basically reset itself.

When I got there they reread some of your info again. And everything had been covered so the guy decided to "smoke it" again and he found a vacuum leak. They had smoked it twice early on in the process. So now I'm driving it as much as possiblle to see if it happens again after the vacuum repair. So based on this last repair said it had to be fixed. If I don't see ther problem again I will come back and rate you guys EXCELLENT! With a bunch of stars and make another donation. Thanks for all of your help and I will recomend this site to anyone that has a problem.

Regards,
Pat
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Monday, September 27th, 2010 AT 1:11 PM
Tiny
MERLIN2021
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  • 17,250 POSTS
Your welcome Pat, glad we could "git er done!"
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Tuesday, September 28th, 2010 AT 10:34 AM

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