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Discussion Starter #1 (Edited)
P0155 and P0135 Codes - need help

I have a 1996 4.6 V-8 Tbird with 105,000 miles and can not solve this ongoing code problem. I have replaced both of the B1 and B2 S1 sensors and I am still getting the codes - P0135 and P0155. I have read many pages of similar problems with the search function. I believe it is a break in the harness? Can someone please help me with specific pins and harness/plug locations to check for shorts. I know this is a repeat request from other members, but can someone repeat this information for me again. I would be very grateful.

I just replaced the MC and Booster and had to disconnect the main harness on the DS of the booster on the firewall would this have contributed to my S1 issues.


Thanks - any advice will be really appreciated.

Glenn
 

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I had this problem, I was scratching my head for months before I finally bit the bullet and pulled the harness up from behind the heads.

This is what I found... http://forums.tccoa.com/showpost.php?p=1298578&postcount=15

The easy way to tell if there are shorts would be to unplug the bulkhead connector next to the A/C accumulator, unplug both the driver's and passenger's O2 sensors and bring the harnesses for each sensor up from behind the engine, then use a multimeter to check the resistance between each of the four pins. There should be an infinite number of ohms between each. If not, there's a short.

The codes turned up for me immediately after I ended up disturbing the harnesses to do a PI cam swap.
 

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Discussion Starter #3
Do you mean to check each of the 4 pins in the sensor connector against ground to detect a short or check the sensor pins with the pins in the bulk head connector (if so which pins)?

Thanks,

Glenn
 

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Check each of the four pins against each other.
 

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Discussion Starter #5
Thanks

Thanks for the information on testing the sensors. I have been working on other projects recently and now I am back to my TBird.

One more question, is there any chance the PO155 and PO135 codes could be referring to a bad CC.

Glenn
 

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CC...?

If you mean PCM, then it has been known that the drivers on the board for the heaters fail, but from what I've seen it's usually all four at once - not just two.
 

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Discussion Starter #7 (Edited)
CC - Cat Converters

If my o2 sensor wiring is good any other thoughts on troubleshooting. Both front o2 were recently replaced. I honestly think my wiring is OK, I closely looked at it and it looks factory perfect - nothing disturbed or altered at the back of the engine. Is it possible that a vacuum leak could cause the emissions light.

No chance it could be the ECU?

Thanks,

Glenn
 

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P0135 and P0155 are heater circuit malfunction codes, not efficiency or rich/lean codes. It means the PCM is not seeing the correct voltage drop across the voltage send and return lines to the heaters in the O2 sensors. There's no chance this could be related to the cats or a vacuum leak, dirty MAF etc. The only components involved with those codes are the PCM itself, wires leading to the front O2 sensors, and the O2 sensor heater elements.

Like I said it's possible it's the PCM, but I've not yet seen an instance where JUST the front two failed. If it is a problem with the harness (which I'm almost certain of), the reason the back two aren't giving codes is because the harness for those runs through the transmission harness, which goes through the dash. The front two go through the engine harness, which runs through the firewall by the passenger shock tower.

Have you checked to be sure there isn't a short between any of the four wires at either front O2? Disconnect the passenger side bulkhead connector and check resistance between each of the four pins on the O2 sensor connector. If any comes back less than infinite, there is a short.
 

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Discussion Starter #9
Brandon:

Thanks very much - I will definitely check the wiring as you suggested. I will post back my results.

Glenn
 

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Like Brandon said, most of the time O2 heater issues are related to the wiring, in my experiences.
 

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Discussion Starter #12
Just wanted to get back to everyone on my O2 sensor issue. What had happened was that my 4.6 plastic ITM had a very small crack at the PS rear. Small amounts of Antifreeze had leaked into the wire harness behind the PS of the rear engine. Over a period of years the antifreeze had deteriorated the wires and totally ate-up the O2 wire insulation. The O2 wires then shorted out causing the CEL to come on. The wires were re-insulated and all is good now.

Thanks for everyone's help in helping me with this problem. It was very hard to find.

Glenn
 

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Figures, sounds like exactly what happened to me. Glad you got it nailed. :thumbsup:
 
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