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Old 04-07-2012, 10:26 PM   #1
saturn_owner68
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2003 L-Series 2.2L Sedan
1996 SL1
Default Check engine light on P0128

The check engine light came on in my 96 saturn, and the code came up P0128 according to the book it says Thermostat rationality error detected. However the car is not overheating. Any ideas on what could cause this code to come up?

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Old 04-07-2012, 10:33 PM   #2
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Default Re: Check engine light on P0128

Quote:
Originally Posted by saturn_owner68 View Post
The check engine light came on in my 96 saturn, and the code came up P0128 according to the book it says Thermostat rationality error detected. However the car is not overheating. Any ideas on what could cause this code to come up?
There is no P128 for a 96 Saturn. Try another code reader or go to a parts store and get it read.

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Old 04-07-2012, 10:48 PM   #3
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Default Re: Check engine light on P0128

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Originally Posted by OldNuc View Post
There is no P128 for a 96 Saturn. Try another code reader or go to a parts store and get it read.
that explains why when my thermostat last epic failed (it would sit between C and 1/4 on the highway on a cold winter's day ) the service engine soon light didn't illuminate...

...
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DOB: 3/19/97
Date Obtained: 5/30/07
Status: Alive, 1/2 exhaust

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Old 04-08-2012, 06:42 PM   #4
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Default Re: Check engine light on P0128

I did take the car to the autoparts store, but they got P0128 to,but they said the computer is giving a false code, is this possible? I also got 2 new codes P0301 and P0303 that would mean misfire is detected, but the car is not misfireing, could replacing the pcm be in the future? BTW as far as the thermostat, the temperature gauge in the car goes to the 1/2 way mark.

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Old 04-08-2012, 07:01 PM   #5
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Default Re: Check engine light on P0128

Quote:
Originally Posted by saturn_owner68 View Post
I did take the car to the autoparts store, but they got P0128 to,but they said the computer is giving a false code, is this possible? I also got 2 new codes P0301 and P0303 that would mean misfire is detected, but the car is not misfireing, could replacing the pcm be in the future? BTW as far as the thermostat, the temperature gauge in the car goes to the 1/2 way mark.
hows your coolant level? is it full? and as far as the codes go wether there
lagit or not. i would reset the computer not with the scanner but taking off
both battery cables right off the battery and touching them together wrap
a small clamp around them to keep them tight and touching together for
1 hour doing it this way will drain down all voltage from the capaciters and
reset your computer totally. try that and post back

...
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Old 04-08-2012, 07:37 PM   #6
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Default Re: Check engine light on P0128

Do not pull battery cables. Just pull the power to the PCM fuse, PCM B in the fuse box, location diagram is in the lid.

You may have misfire codes and never feel the misfire so do not assume that they are bogus.

What brand and type of spark plugs are you using? Cylinder 1 and 3 fire on the same polarity and this sounds like an ignition issue.

The PCM does not generate false codes, it is a scanner software issue.

Does the temp gauge increase to 1/2 as the engine warms up or go immediately to 1/2?

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Old 04-08-2012, 08:02 PM   #7
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Default Re: Check engine light on P0128

he could have a computer glitch just like home computers get glitches
and when You reset it by turning it off and back on again it clears itself. and oldnuc whats wrong with taking the battery cables off and touching them together for an hour to reset it that way? just to see if it will clear the engine light after all its a fresh start for the PCM.

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Old 04-08-2012, 08:08 PM   #8
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Default Re: Check engine light on P0128

Quote:
Originally Posted by OldNuc View Post
Do not pull battery cables. Just pull the power to the PCM fuse, PCM B in the fuse box, location diagram is in the lid.

You may have misfire codes and never feel the misfire so do not assume that they are bogus.

What brand and type of spark plugs are you using? Cylinder 1 and 3 fire on the same polarity and this sounds like an ignition issue.

The PCM does not generate false codes, it is a scanner software issue.

Does the temp gauge increase to 1/2 as the engine warms up or go immediately to 1/2?
As far as spark plugs I've got bosch platnum spark plugs I put those in at 200,000 miles so the spark plugs have 26,000 miles on them. As well as the spark plug wires. As far as the temperature gauge it goes to 1/2 slowly as the engine warms up.

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Old 04-08-2012, 08:17 PM   #9
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Default Re: Check engine light on P0128

Change the plugs and wires to NGK BKR5ESA-11 plugs and that will fix the misfire.

Find the vacuum leak. Whoever is reading the codes is using defective software... I would bet the correct code is a P507.

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Old 04-08-2012, 08:50 PM   #10
saturn_owner68
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1996 SL1
Default Re: Check engine light on P0128

Quote:
Originally Posted by OldNuc View Post
Change the plugs and wires to NGK BKR5ESA-11 plugs and that will fix the misfire.

Find the vacuum leak. Whoever is reading the codes is using defective software... I would bet the correct code is a P507.
Thanks for the help, who would of thought napa autoparts would be wrong. I see you can get the spark plugs you mentioned from Amazon, so I will try those. As far as a vacuum leak I will look for that.

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Old 04-08-2012, 09:26 PM   #11
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Default Re: Check engine light on P0128

Plugs and wires will get rid of the 301 & 303 and finding and fixing the vacuum leak will get rid of the high idle and probably the other incorrectly read code. Pull the PCM B fuse after the plugs and wires are changed and see what comes back. Be sure to clean off the aluminum coil tower terminals as well. Use something like a damp kitchen combination scotch-brite and sponge.

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Old 04-09-2012, 02:59 PM   #12
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Default Re: Check engine light on P0128

Quote:
Originally Posted by saturn_owner68 View Post
Thanks for the help, who would of thought napa autoparts would be wrong. I see you can get the spark plugs you mentioned from Amazon, so I will try those. As far as a vacuum leak I will look for that.
Advance Auto also carries NGK spark plugs... see if you can go to one without having to wait nearly a week with shipping and such..

...
97 SL2
DOB: 3/19/97
Date Obtained: 5/30/07
Status: Alive, 1/2 exhaust

2004 Merc G.Marquis GS
DOB: 2/4/04
Date Obtained: 7/6/12
Status: Alive, no heat

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Old 04-11-2012, 01:17 AM   #13
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Default Re: Check engine light on P0128

I took the car to autozone and had them read the codes, their machine gave a P0404 code and P0350 code, so I replaced the EGR valve and coil pack so far the check engine light went out and has not come back on. Even though the check engine light is out, it probably would be a good idea to change the bosch spark plugs to NGK ones.

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Old 04-11-2012, 06:18 AM   #14
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Default Re: Check engine light on P0128

I would suggest that action as the Bosch plugs are probably responsible for the ignition system failure. Aftermarket ignition parts are not real reliable and used JY parts have better life so if you have coil-ICM problems in the future use JY parts.

There is no P350 either so I take that as either a typo or more bad scanner data.

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