My check engine light is on all the time. I went to Auto-Zone and they checked the codes. I had 4 codes: Bank 1, Sensor 1 OX. Same on the second code but Sensor 2, then it repeats.

The engine runs fine, has plenty of power, is not missing or bogging down... I have a few questions.

What are the odds that both sensors are bad and how do I test that short of buying and installing new sensors?

What else short of bad sensors cause this engine code? Bad spark plug wires or plugs? Anything else?

Thanks,
Bob

 

How many miles do you have? If its up there, you may just want to replace both of them.

And spark plugs and wires will not set off that code, unless it says too rich or too lean. If one of the codes is p0138 it is O2S above normal voltage or something like that. Which is strictly related to the sensor itself.

Someone will have a better answer than me, but I just had a similar problem.

 

Sorry, didn't know the codes themselves were important.

P0132 - Bank 1, Sensor 1
P0138 - Bank 1, Sensor 2
P0135 - Bank 1, Sensor 1
P0141 - Bank 1, Sensor 2

 

P0132 (M) 1/1 O2 Sensor Shorted To Voltage Oxygen sensor input voltage maintained above normal operating range.

P0138 (M) 1/2 O2 Sensor Shorted To Voltage Oxygen sensor input voltage maintained above normal operating range.

P0135 (M) 1/1 O2 Sensor Heater Failure Oxygen sensor heater element malfunction.

0141 (M) 1/2 O2 Sensor Heater Failure Oxygen sensor heater element malfunction.

it sounds to me like both o2's need wiring help. sad day =[

 

Thanks for the informative answers guys. Sad day indeed.

I'll get started on tracing the wires back tonight. Do you know if I unplug the sensor what I should be seeing across the wires going back to the computer? i.e. open, shorted, voltage, or a certain resistance? (other than shorted, obviously)
Or should I start at the computer and measure that end first for clue?

Bob

 

I started at the sensor and it tested at out at 5.3 ohms. Factory spec is 4.5 ohms at 70 degrees F. Considering it was 92 degrees, I think this is probably in spec. I then checked the harness going back towards the computer. It was only a weak 4 volts. Hmmm...

Up at the fuse box with the ignition on "run" I pulled the forward Ox sensor relay and tested voltages. I had 12 volts on the coil side of the relay so the relay should be firing. I hooked the relay up to 12 volts and checked continuity on the correct pins. It tested good. But, with the relay pulled I could not get twelve volts on either pole of the switched side of the relay. Hmmmm...

So I backed up to the fuse block and tested all the fuses. this is really easy with a volt meter. You hold the negative wire to the negative battery post and then touch the positive lead on the volt meter to BOTH sides off each fuse. A little of each leg protrudes on both side of the fuses on top. They all tested good, but then I noticed that one fuse socket had the clips to hold a fuse but had no fuse. It was a 20 amp according to the schematic in the lid of the fuse block. Hmmm....

I replaced the fuse and then retested both poles on the switched side of the relay, and imagine that, one pole had 12 volts on it, just waiting on a plugged in relay to pass the current to the sensors.

I hooked the sensor back up and drove it around for about 15 minutes but the engine light still stayed on. Hmmm...

Tomorrow I will have Auto Zone read the codes again and see if at least one of the sensors has corrected itself now that it is getting heater voltage. Otherwise I have only fixed 1/2 of the problem.

My guess is the PO pulled the fuse in the hopes that it would get rid of the check engine light, but it didn't work
(DUH!), and the real problem is the sensors themselves.

Tomorrow is another day.

 

After replacing the fuse the computer was still throwing the same codes. So I bought the OX sensors and installed them. Bad news is, the engine light is still on. I drove it around for about a 1/2 hour and reset it using the odometer trick but it is still lit.

Any ideas why it might still be lit? Tomorrow I'll have the codes read again and see what they say. This is getting expensive.


On a good note, the engine is running smoother and has gained some horsepower in acceleration.

 

They cleared the codes at the shop and it has been fine for three days. Good to go!