My 2002 Discovery's catalytic converters were stolen while parked on the street and were replaced with new cats along with two different and new upstream Oxygen sensors. One sensor brand is UP 234-4620 (for 98-02 Honda and 98-04 landrover), and the other oxygen sensor is Denso 234-4694 (for 99-04 landrover). Multiple check Engine light codes came on. 1) PO130 - Oxygen circuit bank 1, sensor 1; 2) PO150 - Oxygen circuit bank 2, sensor 1; 3) PO100 mass airflow circuit; 4) PO400-exhaust gas recirculating;5) PO011-camshaft over advance bank 1.

The car is running well except for the check engine light codes

Please help by explaining the followings:

a) I do not understand why the second code PO150 says oxygen circuit bank 2, sensor 1 (why not sensor 2 ???)

b) Both the first and second oxygen sensor codes are related to sensor 1, no code related to sensor 2. could it be sensor 1 circuit was not being read due to bad oxygen sensor OR due to break in wiring when the thief yanked out the O2 sensor 1 harness along with the catalytic converter

c) can the oxygen sensor wire harness 1 and 2 be checked by measuring the ohm resistance or voltage in the harness while the engine is running or not running? Can a wire continuity be checked as well for the oxygen sensor harness (this will require access to the oxygen harness on the engine side?)

d) Which side of the engine is bank 1 ? driver side or passenger side? I donot remember which side has which oxygen sensor. I have two different oxygen sensors. One is Denso, and the other is UP (cheaper of the two)

e) Are the other engine codes only caused by the sensor 1? Am I correct to say that P0100, P0400, and P0011 will go away after i successfully repair or replace the oxygen sensor #1

All comments are welcomed. I am in a little jam because car did not pass smog and registration expires in 7 days.
Thank you

 

a. Sensor 2 is only related to cat efficiency - new cats mean no issues.
b. Yes, codes could be due to thief yanking wiring or bad sensors.
c. Yes. Sensors have four wires. Two are ground and hot for heater circuit, two are for ECU voltage. Heater circuit open or short will throw a separate code. Because you don't have that I would guess you have bad sensors out of the box and not bad wiring.
d. Drivers side. Both sides have two sensors for a total of four. Sensor 1 is always upstream of cat, sensor two is downstream. Bank 1 sensor 1 is upstream drivers side.
e. Possibly, but more commonly related to bad MAF.

If you have android, get elm327 from Amazon and free torque app. Chart sensor voltages, they should oscillate, if they do not sensor or wiring is bad. If one does and one does not, swap side to side to validate sensor or wiring.

Use torque app, clear codes. Disconnect MAF and see if other codes go away. Reconnect MAF and if they come back and runs bad you have bad MAF.

Good luck.

 

Thanks so much for your prompt response and I must say you have good logics. I am trying to understand and figure out your logics.

1) Which engine trouble code is for open heater circuit or short? Since I do not have those codes (Thanks goodness. replacing harness is much more difficult than replacing sensors)

2)Car is running very well. Can it be a MAF problem? (will try running it with MAF disconnected and report back)

3) Your qoute: "Two are ground and hot for heater circuit, two are for ECU voltage" just for clarification: Two wires are ground? One hot wire is for heater circuit? and the other one hot wire is for ECU?
what wire color related to each of these four wires?

4)What brand and part number is the recommended O2 sensor for a 2002 LR discovery?

5) is each O2 sensor same for upstream and downstream on both sides?

Thaks again and looking forward to your wisdom

 

3. You are slightly misreading Extinct's response. "Two are ground and hot" -- the "two" refers to the pair of wires. There is only one ground. The other pair of wires is the ECU signal. I know that there are threads on this forum that explain the wire colours.

4. I have not read of the UP sensors before. Walker brand sensors seem to have a good reputation and a low failure rate.

5. Upstream and downstream sensors are different, but each side is the same for each position. Walker 350-34462 is upstream left or right; Walker 350-34188 is downstream left or right.

 

Thanks for the info.

 

Thanks for the info.
1) What would be the best way to properly measure voltages from each oxygen sensor (upstream?) while engine is running? Use of voltage probe Poking through the wire insulation while sensors still plugged in and engine running? Will this cause any bias voltage which will give false voltage readings?

2) Did the factory use Walker and Bosch as the original O2 sensors? My local autozone part store sells Bosch O2 sensors and Denso O2 sensors. What is your opnion on Bosch and Denso? BY the way I just found that from ebay seller what I bought was not a denso. It was an API on one side and UP on the other side.

3) If the O2 sensor wire harness was bad due to open or short circuit, what would be the engine code for that?

Thanks again

 

A decent OBD2 reader should be able to show you the live voltages from the O2 sensors. They are measured while the engine is running.
The factory sensors would have been Bosch. People were reporting a very high failure rate of replacement Bosch sensors about one to two years ago, while the Walker sensors seemed to have a much better track record. I have used them for all of my replacements without any trouble.

 

Mollusc,
Very valueable info.I will try to get two new upstream Walker sensors and test again.
I have an old Innova 1003 scanner which does not read voltage. Someone suggested that voltages can be measured at the ECU except I need to know where the ECU is and which wires to measure.

CAn i simply disconnect the sensor utput and measure the voltage directly while the engine is running to see if sensors are any good? I may also have bad wire harness when my catalytic was stolen.

 

Get a $10 ELM327 from Amazon and use the free torque app for Android to chart the voltages, total investment less than $10

 

I had issues with O2 sensors for years. A month ago I put in four new NTK sensors I picked up on Amazon. First time in five years I have zero engine codes. The sensors weren't cheap, but they work.