: O2 sensor trouble codes after engine installed

03-27-10, 09:28 PM
I took the Devile out for the first time after I studded the block.....and now I am fixing little things....like the O2 sensors..This is what I got

p0174-System to lean bank 2
p0300-random misfire

along with rough idle.....other than that, it runs ok

1997 Deville Concours

03-27-10, 10:05 PM
p0174-System to lean bank 2
Check for a vacuum leak. Maybe the PCV valve grommet.

See Ewill's posts here.

03-28-10, 04:55 PM
Found out what was wrong! I forgot to hook up a ground wire below left side of engine...and also had 2 coil packs that were not functioning right....Now it doesn't skip a beat at all:yup: Runs like a champ......Ryan

03-30-10, 10:53 PM
Ok...maybe I didn't find out what was wrong.....The same codes are now back on....Car runs fine.......I originally added more wire to the ground wire so I could ground it out on something solid..The original connector snapped off when I took out the engine...Codes did go away, but shortly appeared again.

All codes read current even when engine is running/not running.....When I go to ground this wire, it will spark a little...so I do have power.

Do you think adding this extra foot of wire is too long?? It is grounding out properly....Maybe this wiring is too sensitive??

Originally this wire connected to the rear transmission to engine bracket (Just below EGR valve)..............also are these 3 codes referring to all O2 sensors except the front exhaust manifold?

I have checked all fuses that are related to O2 sensors....I have even looked at wiring diagrams.......These sensors are driving me crazy:mad2:

Below is a grounds diagram for the O2 sensors


03-31-10, 06:30 AM
I have no idea if this is relevant, but the O2 sensor troubleshooting trees tell you not to bend, kink, or alter the sensor wiring as it is part of the sensor circuit "tuning". There's also something about one of the wires being a ground "clean air reference", so maybe if your new wire changes the resistance of the O2 sensor ground circuit, it might throw a code.

Mind you, this is a SWAG (Scientific Wild Ass Guess)

03-31-10, 09:05 AM
i've been having pretty much the same problem. My car has 4 O2 sensors and 3 of them keep throwing heater performance codes. It runs fine some times, ok some times, and like ass some times. Very intermittent.... always the same codes. Something ive been half-ass working on for a while now. Ill take a look at my wiring based on your diagram later today :)

Edit: keep on top of it. I've been at mine for a long time. Every time i change something it seems like its fixed and then "Ok...maybe I didn't find out what was wrong.....The same codes are now back on".

03-31-10, 09:12 PM
I do have a standard obd2 scanner that is capable of Live Data....What should the volts be on these sensors........Ondemand5 (which is where I get all my stuff) tells something about 1 and 0 volts?? ....I don't understand.....My scanner is telling me that I'm getting some kind of volt measure on these sensors....some of them are .54 V......anyways if I'm getting some kinda of reading then they must be working, or barely working...Right???

Ondeamand5 does mention something about altering wire.........I guess I'll try some extremely short wire........it's a pain in the ass trying to reach down there and tie together wires.

As of right now I'm getting 23 MPG on highway and now have a too lean code that has showed up.

Sometimes I get 1 current code. Others days I get 3 current codes all at once......What is happening:crying2:

If I can't figure this out soon......I guess I'll have to take it to the local dealer and have them figure this out...........Thanks again Ryan

04-01-10, 09:52 AM
so according to that picture, the O2 sensor heaters share a common ground.

FSM says P0135 is:

DTC P0135 HO2S Heater Performance Bank 1 Sensor 1

your post says:


I also have P0135. Add P0155. Another similarity between mine and yours is that i have 3 out of 4 sensors malfunctioning. I would think that if it was a ground issue, all 4 sensors would be misbehaving. I have never had a code for my post-cat sensor. (if i remember right... it might be the pre-cat). I think my third code was P0147 but it hasnt popped up in weeks so not 100% sure. Its probably in a post in here somewhere... Basicly same situation. Mine hasnt run perfect since the engine was replaced. Something not put together right i think. Im getting voltage at the sensor according to spec in the FSM. I have a sway bar link to replace today, will see whats left over and ill look for a good meter to do more tests.


This diagnostic test is used to determine if the heating element in the rear oxygen sensor is operating properly. An oxygen sensor acts as a battery because it creates its own voltage once it reaches operating temperature. This voltage is produced when the oxygen content in the exhaust stream is different than that in the atmosphere. The heating element is energized through CKT 139 when the ignition is ON and allows the oxygen sensor to reach operating temperature quickly. This in turn allows the PCM to enter Closed Loop fuel control quicker. When cold the voltage that the PCM measures on the HO2S HI and LOW inputs is called bias voltage. If it takes too long for the HO2S to very above or below the bias voltage within a specific time since key ON DTC P0135 will set.

Failure Condition
The PCM monitors the rear heated oxygen sensor input to determine when its voltage becomes either 151 millivolt less than or 151 millivolt greater than average rear heated oxygen sensor bias voltage for 0.1 second. If it takes too long, DTC P0135 will set.

Im not sure if i can paste the diagnostics procedure or not, ive seen people do it but is it allowed?