Heated oxygen sensor

[Wolfman1505]

Hello,

Im having a P0134 error. The manual told me that the Heated Oxygen Sensor has a open circuit.
But i cant find the Heated Oxygen Sensor. I have looked in my manual but with no luck.

Can anybody tell me where i can find the H.O.S.

And can can someone tell me in a few simple words what that thing does? My car runs normal. Do i need to fix this soon or is it not so importend?

[LMP]

THe engine computer has 2 calculations modes for fuel: open mode: measures amount of air (MAF) and precalculates (based on standard proportions and temperature/throttle position...) amount of injection needed. THis calculation is on the safe side, meaning it wants at least to ensure that the engine will run normally ..which is what you have just said, generally a little richer than actually needed.
Mode 2 is "closed loop": once engine is warm enough, the oxygen sensor measures the actual amount of oxygen left in exhaust and determines from that if the "safe" calculation was a little too rich or a little too lean...and computer applies corrective action accordingly to amount of injection. If HOS is found "not operative", the computer stays in "safe" mode...which can result in a slightly increased fuel consumption, but the engine runs anyway. Depending on the amount of "safe" miscalculation, there are opinions that it could damage the catalyser but I cannot advocate on that; however, passing an EPA test might be a risk.
If engine is a 3.8, the Heated Oxygen Sensor is sandwitched above transmission near firewall on rear exhaust manifold, a cumbersome place to look at.
www.avigex.ca/xport/02wiring.jpg

[cdru]

Originally Posted by LMP

If engine is a 3.8, the Heated Oxygen Sensor is sandwitched above transmission near firewall on rear exhaust manifold, a cumbersome place to look at.
www.avigex.ca/xport/02wiring.jpg

tHE 3.1 and 3.4 will be in the same location. On the 3.4, you can get to it to replace it either by going up from underneith by way of the gap between the floorpan and the exhaust pipe, or from above by removing the coil pack and rocking the engine forward.

[Wolfman1505]

Thanks for yours answers.
I had taken my laptop for a ride and recorded the DTC.

At home a had a look at the recorded DTC.
In the beginning the HOS was open but afther a while he went to close.
He stayed closed for a few seconds and then open again. This happend reguerly.

So i wonder now, does he work normal? Or should he stay closed all the time when headed?

nicke66 thanks very mutch for the interface cable and software. It works just great!

[nicke66]

Originally Posted by Wolfman1505

Thanks for yours answers.
I had taken my laptop for a ride and recorded the DTC.

At home a had a look at the recorded DTC.
In the beginning the HOS was open but afther a while he went to close.
He stayed closed for a few seconds and then open again. This happend reguerly.

So i wonder now, does he work normal? Or should he stay closed all the time when headed?

nicke66 thanks very mutch for the interface cable and software. It works just great!

I have emailed the Diagnostic chart for the P0134 to you. I do not know if you have got any service manual yet. I have also emailed it to LMP, please host it on www.avigex.ca/xport/.

With this chart, you should be able to decide if the sensor or the wiring is the cause of P0134.

[LMP]

Diagnostic chart for P0134 compliment of nicke66
www.avigex.ca/xport/DTC_P0134.jpg

[Wolfman1505]

Thanks again.

But i allready have my own factory manual.

Now the problems are getting wors.
Yesterday i had a short ride and suddenly the engine stalled for a traffic lite. It happends all the time now once te engine is heated.

The DTC tells me P0101. Mass Air Flow.
But there is no P0134 error?

The only thing i have done is checked te wire's and harnes. Losend some connections to inspect them.

I dont have any contactspray at home right now.
I will get some and spray all the connections.
I dont think there is something wrong with any part. It must be the wireing.

[Wolfman1505]

I have sprayed some connections with contactspray.

Then i started te engine. It did nor run well but he didnt stall enymore.
In the eavening i had to go someweher and took the Pontiac.

In the beginning he run normal. But when i wanted to pek the car he stalled. Driving afther that was almost inpossible. I had a hard time getting hem up to 2000 rpm. But once he was he run normal. But afther every stop he stalls.

Today i had a closer look to the wireing. And i found the problem. The yellow wire to the MAFz was almost broken. I put the wire in a position so he made contact again and taped it.

Now the car runs with no problem at all. So no i have to look for a new connector. The wire broke just above the connector. There is no room for repair.

So im back to my usual problem The P0134. HOS Open curcuit.
I drove my car for about 15 min. And recorded the DTC. When i drove of the HOS closed. It stayed closed for about 4 min. Then he opend. Afther that he is most of the time open, but sometimes close for a few seconds.

My question is what should be normal behevoir?
Whe the engine heates up should he stayed closed?

[LMP]

Running without proper MAF sensor had certainly upset the mixture and this may have also modified the "long time constants" in the ECM (calculation constants that adapt to and keep long time corrections provided by the HOS ).
I want to be sure when you are talking of "open" that you refer to "open" HOS circuit and not to the "open" and "closed" loop operation that you may probably see from your scanner too.
In as much as the HOS is concerned, I'd expect it to stay ON all the time once up to temp. I know it has to maintain a certain temperature to operate, but I see no indication that the "heater" section is thermostatically controlled, and that the sensor could be maintained at temperature by the exhaust itself...I am in fact puzzled by this on and off condition.
ONe thing I'd do however is disconnect battery for 10 min with headlights ON (to sink any residual charge) to reset the ECM constants to default value, ( may be you can do that from the scanner too). WOnder if the scanner interface works also with '93 OBD1...I'd surely hook up my portable to have a glance too.

[nicke66]

Originally Posted by LMP

Wonder if the scanner interface works also with '93 OBD1...I'd surely hook up my portable to have a glance too.

Yes, it does, as long as you have the 3.8 engine. The interface and software supports all Trans Sport 3.8 1992-1995 (and also the export version with the quad 2.3 engine 1993-1996, sold in Europe). It also probebly supports the Lumina APV and the Silhouette.

The airbag and ABS software also works for 3.1, but the 3.1 ECM uses 160 baud ALDL, and need some other interface and software.

[Wolfman1505]

Originally Posted by LMP

Running without proper MAF sensor had certainly upset the mixture and this may have also modified the "long time constants" in the ECM (calculation constants that adapt to and keep long time corrections provided by the HOS ).
I want to be sure when you are talking of "open" that you refer to "open" HOS circuit and not to the "open" and "closed" loop operation that you may probably see from your scanner too.
In as much as the HOS is concerned, I'd expect it to stay ON all the time once up to temp. I know it has to maintain a certain temperature to operate, but I see no indication that the "heater" section is thermostatically controlled, and that the sensor could be maintained at temperature by the exhaust itself...I am in fact puzzled by this on and off condition.
ONe thing I'd do however is disconnect battery for 10 min with headlights ON (to sink any residual charge) to reset the ECM constants to default value, ( may be you can do that from the scanner too). WOnder if the scanner interface works also with '93 OBD1...I'd surely hook up my portable to have a glance too.

I was talking about open en closed loop. Its what i see on my laptop.
I just went for a short ride again and he returnt the P0134 error again.
When i was looking under the hood a friend walked by. I showed him how the software worked and that i noticed that the HOS was in open loop en the CEL was on. Whe i hit the trottle at 3000 rmp the open loop changed to closed. And the CEL went off.

I will reset the ECM in a short while with my software and let you know.

[LMP]

OK this is a lot clearer now. While switching to open or closed loop operation is obviously linked to the HOS here because P0134 shows, other factors can make or break closed loop operation. "closed loop" operation is same as "feedback" operation and means computer takes HOS reading into account when adjusting injection. If is does not for any reason, even with no HOS problem (like when engine is cold) the system works in OPEN LOOP, either with raw default values or calculating "feed forward" values using info from MAF, throttle position and temperature readings.
Condition specific to set P0134 is obviously 3rd one (HO2S voltage steady between 350 and 457mV) cause all other conditions are there to establish that the engine is in normal operating regime. I think "diagnostic aids" tells all that can be done to pinpoint the problem.
My suspect: the HOS heater is dead, for internal or external (wiring, connectors) causes.

ABout constant values (LongTerm fueltrim and Short term fueltrim) since you have the scanner you can read these. a value of 128 is "neutral" meaning no correction . Below 128 means there is a correction for too rich a mixture, while above 128 means correction because too lean a mixture exists. I would be interesting to note that before changing or erasing them.

[Wolfman1505]

Originally Posted by LMP

OK this is a lot clearer now. While switching to open or closed loop operation is obviously linked to the HOS here because P0134 shows, other factors can make or break closed loop operation. "closed loop" operation is same as "feedback" operation and means computer takes HOS reading into account when adjusting injection. If is does not for any reason, even with no HOS problem (like when engine is cold) the system works in OPEN LOOP, either with raw default values or calculating "feed forward" values using info from MAF, throttle position and temperature readings.
Condition specific to set P0134 is obviously 3rd one (HO2S voltage steady between 350 and 457mV) cause all other conditions are there to establish that the engine is in normal operating regime. I think "diagnostic aids" tells all that can be done to pinpoint the problem.
My suspect: the HOS heater is dead, for internal or external (wiring, connectors) causes.

ABout constant values (LongTerm fueltrim and Short term fueltrim) since you have the scanner you can read these. a value of 128 is "neutral" meaning no correction . Below 128 means there is a correction for too rich a mixture, while above 128 means correction because too lean a mixture exists. I would be interesting to note that before changing or erasing them.

The HO2S voltage is 448 or 452. No other value's.
LT feultrim is 130 then going up to 150 to 159. In drive its either 150 or 159. Sometimes he drops back to 128 but realshort.
ST stays steady at 128.

I have no idea what that tels me?
Im hoping you are going to explane that now....

[LMP]

[quote=Wolfman1505]The HO2S voltage is 448 or 452. No other value's.
LT feultrim is 130 then going up to 150 to 159. In drive its either 150 or 159. Sometimes he drops back to 128 but realshort. ST stays steady at 128. QUOTE]
Surprises me...and not....I'd see the short term changing fast, with LT almost steady, but having the longterm changing while the short term says the same is at least unusual.... . SHort term responds quickly to changes in measured O2 (when the HOS value changes..which is not your case) and..if those values stay for a long time, they will increment the long term correction eventually up to (or down to) the ST value....

HO2S voltage steady at 450 +/- 2 mV is not OK and explains short term is steady, and as described above this sets the P0134 alarm. It should vary largely between 200 and 900 mV with quick changes in throttle. 450 is the voltage the ECM supplies to the HOS....should be that value even with a disconnected HOS. Problem is really around there. ANyway you could measure presence of heater current? like "ungrounding" wire C at HO2S connector and installing ammeter there..between C (from HOS) .. to ground..should read a few amps....

[Wolfman1505]

Hmmm seems i did something wrong here....

See next post.