misfire cyl1 and exhaust leak followed by mil light on for pre-cat o2 sensor

douellette

Original poster
Member
Aug 26, 2012
15
so this TB has had an exhaust leak for probably 3-4 years (in the manifold). The guy (recently, maybe 2 months ago?) replaced the #1 coil but didnt plug the plug on right so it wasnt firing, threw a misfire code. He ran it like that for only a couple days i wanna say since he didn't want to drive it with the misfire. he did drive it from his house to mine, which is probably a 10 minute drive. Anyway, i cleaned the throttle body. Now the check engine light is on the o2 sensor voltage reading high, P0132. I used the Torque app on my phone with a ELM Bluetooth reader to watch the o2 sensors and they both seem to be copying each other, like as if the cat isnt working, but it hasnt thrown a code for the cat. So what do you guys think?

also, when i cleaned the throttle body and reinstalled im not sure if it did the relearn procedure right because there is 2 codes in there for it P1120 and P1220. it also says throttle position at idle is like 22% but it is idling where its supposed to be. Problem?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The front O2 sensor should wiggle up and down around once a second. The post-cat sensor should be rock steady. If the post-cat sensor wiggles at all, then it's like the cat isn't operating, and that will eventually throw the "low cat efficiency" code. Not always instantly.

You have to disconnect the battery (or pull the proper PCM fuses) to force the relearn, and then just drive around for a while. The throttle PLATE can be 22% open without a problem IIRC, but the fuel injector pulse width will control the idle RPM.
 

douellette

Original poster
Member
Aug 26, 2012
15
the roadie said:
The front O2 sensor should wiggle up and down around once a second. The post-cat sensor should be rock steady. If the post-cat sensor wiggles at all, then it's like the cat isn't operating, and that will eventually throw the "low cat efficiency" code. Not always instantly.

You have to disconnect the battery (or pull the proper PCM fuses) to force the relearn, and then just drive around for a while. The throttle PLATE can be 22% open without a problem IIRC, but the fuel injector pulse width will control the idle RPM.

well ive done pcm fuse pull when i did the throttle body. but i cant drive it around since it doesnt have plates/isnt registered (im selling it for someone i know). would the exhaust leak cause it to run rich...damaging the cat? because i dont want to replace cat and have it go bad after a week.
 

SAR85

Member
Jan 31, 2012
74
While it is true that the cat may not be cleaning the exhaust effectively, it does not seem that it would cause any of your other symptoms with the O2 or throttle body codes.

I suggest you download the service manuals: http://gmtnation.com/f23/need-service-manuals-get-them-here-371/, then find the troubleshooting sections for P1120 and P1220. In addition to what you may find there, be aware that the fan clutch shares a reference with the throttle body and accelerator position sensors and malfunctions in the fan clutch wiring can affect those systems as well (if I remember correctly; if not I'm sure someone will correct me!).

If you're willing to dig in to the wiring, the throttle position sensors should read between 0.27V and 4.67V for sensor 1 and 0.31V-4.7V for sensor 2 while the pedal is at rest with the engine off (but ignition on). Also, the reference signal should be 5V. You will need to look at the schematics for which wires to test.

As far as the O2 sensor, it is interesting that the service manuals say that P0132 will not set with P1120 or P1220 set. Regardless, it may be an intermittent problem if your scantool (Torque) data look okay. The manuals say to ensure that the O2 sensor voltage is not greater than 946 mV and that the high signal circuit for HO2S 1 is between 350-550 mV on the PCM side.

There is a bulletin for a P1120 and P1120 due to chafing and subsequent contact of wires with the PCM mounting bracket, which calls for inspection of the PCM harnesses if the DTC diagnostics do not fix the problem. Since you also have this O2 sensor issue (which could also be a problem with wiring to the PCM), it may be worth checking the wiring into the PCM for any broken/chaffed wires.
 

douellette

Original poster
Member
Aug 26, 2012
15
thanks man, ill give that manual a shot. really trying to avoid spending money on the manifold or converter haha since im just selling this for a friend.
 

douellette

Original poster
Member
Aug 26, 2012
15
SAR85 said:
While it is true that the cat may not be cleaning the exhaust effectively, it does not seem that it would cause any of your other symptoms with the O2 or throttle body codes.

I suggest you download the service manuals: http://gmtnation.com/f23/need-service-manuals-get-them-here-371/, then find the troubleshooting sections for P1120 and P1220. In addition to what you may find there, be aware that the fan clutch shares a reference with the throttle body and accelerator position sensors and malfunctions in the fan clutch wiring can affect those systems as well (if I remember correctly; if not I'm sure someone will correct me!).

If you're willing to dig in to the wiring, the throttle position sensors should read between 0.27V and 4.67V for sensor 1 and 0.31V-4.7V for sensor 2 while the pedal is at rest with the engine off (but ignition on). Also, the reference signal should be 5V. You will need to look at the schematics for which wires to test.

As far as the O2 sensor, it is interesting that the service manuals say that P0132 will not set with P1120 or P1220 set. Regardless, it may be an intermittent problem if your scantool (Torque) data look okay. The manuals say to ensure that the O2 sensor voltage is not greater than 946 mV and that the high signal circuit for HO2S 1 is between 350-550 mV on the PCM side.

There is a bulletin for a P1120 and P1120 due to chafing and subsequent contact of wires with the PCM mounting bracket, which calls for inspection of the PCM harnesses if the DTC diagnostics do not fix the problem. Since you also have this O2 sensor issue (which could also be a problem with wiring to the PCM), it may be worth checking the wiring into the PCM for any broken/chaffed wires.

i do also know that there is 2 wires going into the plug on the throttle body that are missing a chunk of insulation (exposed wire). dealership supposedly fixed this wire further up the wire before also. should i just throw some electrical tape over that?
 

McGMT

Member
Jun 17, 2012
621
douellette said:
i do also know that there is 2 wires going into the plug on the throttle body that are missing a chunk of insulation (exposed wire). dealership supposedly fixed this wire further up the wire before also. should i just throw some electrical tape over that?

tape is fine as I understand it is for sale, if I am wrong and it is a keeper a cut and resolder with heat shrink would be much much better.
 

douellette

Original poster
Member
Aug 26, 2012
15
McGMT said:
tape is fine as I understand it is for sale, if I am wrong and it is a keeper a cut and resolder with heat shrink would be much much better.

i will do that since it is for sale, i will probably try to go check out the wiring as was suggested as well.

and i couldnt find the diagnostic procedure for the 2 trouble codes in the service manual, do you know what page/section its on?
 

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