D2 O2 sensor diagnosis help

[agbuckle98]

2002 D2. O2 sensor bank 1 upstream causing check engine light. I replace sensor, it is unresponsive. I get new sensor thinking initial replacement was faulty, still no response from the sensor. I swap upstream sensors side to side, problem stays with bank 1. Now I'm into RAVE wiring diagrams. There is 12v on the NK wire to the O2 sensor with the key on, good. I have good continuity on all 3 remaining pins right to C0635 on the ECM. Should I now look into ECM replacement? If I get a loaner ECM from a buddy, can I just plug and play or is this going to be a T4 / Autologic thing?

 

[roverMc]

Look inside the plug for oil and dirt build up. Mine would play hell with me everytime I washed the engines. Finally removed the stock plug and replaced it with butt-connectors.

 

[agbuckle98]

I checked continuity through the connector all the way to the ECM, the problem unfortunately lies deeper than that.

 

[roverMc]

I checked continuity through the connector all the way to the ECM, the problem unfortunately lies deeper than that.

Sorry bout that. It's beyond me then.

 

[mbrummal]

See if you can borrow a scanner with real-time data. See what it says the O2 voltage is. If it doesn't show it and you are actually getting a voltage at the sensor (check with volt meter) then it is probably a bad ECU. Check for corrosion in the circuit boards.

 

[scottagnew101]

I'd say bad ECU. Same thing happened to me. I had 2 O2 sensors "stuck" on a fault, and could not get them to clear.

 

[baddmojoii]

ECU's are rarely the problem... Continuity/resistance tests are somewhat unreliable as you can have one strand of wire that will show good continuity/resistance, but is unable to carry an actual signal. Loose pin connections can cause this scenario as well. Voltage drop testing of wires is a much better method. My recommendation is to check the pins tension or worst case scenario, run an overlay on the wires to the ECM. Also, it's entirely possible that you have gotten another bad 02 sensor... where did you buy the part from? Is it from LR or from a parts store?

 

[scottagnew101]

ECU's are rarely the problem...

ok that may be the case but based on what he has said I strongly think it is. I have been there in the same situation. Have you?

 

[baddmojoii]

ok that may be the case but based on what he has said I strongly think it is. I have been there in the same situation. Have you?

Not to dismiss your experience, but I can say that I've got a little more than most when it comes to Disco IIs. I'd be curious to know whether the 02 sensor replacement has "Made in Germany" stamped on the sensor body or not.

 

[agbuckle98]

ok, that's a wrap! new ECU was the ticket. Well, new to me that is, I got a loaner from a buddy, took the truck to my local shop and swapped it, everything is fine. I'm going to pick one up from a wrecking yard tomorrow, didn't have time to get there today before close.

 

[baddmojoii]

Congrats on getting it diag'd. It's suprising for the ECU to be faulty, but it's also possible that a faulty 02 from previous shorted out the computer. Be sure to check to see if your Disco had LEV (Secondary Air Tubes going into the heads) and get the right ECU to match, otherwise you'll have to get someone to try to get the proper software loaded into the module to keep from turning on a check engine light.

 

[scottagnew101]

Not to dismiss your experience, but I can say that I've got a little more than most when it comes to Disco IIs. I'd be curious to know whether the 02 sensor replacement has "Made in Germany" stamped on the sensor body or not.

How would it not be the ECU, when you replace the sensor with a new one, then swap a known good sensor with a bad one and it doesn't follow the sensor?

 

[agbuckle98]

picked up my "new" ECM today, had it installed, and have been driving it around all day, no issues, no CEL, and since I ended up with 2 good O2 sensors during my initial diagnosis, I decided I might as well just have both new ones in there as well. Maybe it's the "new parts high" but I think it runs better and a whole day worth of errands only used about a 1/4 tank. Maybe it's getting less crappy mileage now too?

 

[baddmojoii]

How would it not be the ECU, when you replace the sensor with a new one, then swap a known good sensor with a bad one and it doesn't follow the sensor?

A wiring issue could cause the same problem. As I stated before, a resistance test of the wires isn't really a good test. Used to see a lot of wiring issues like that on DII's. Most of the time it was in the vehicle side of the 02 sensor connector. Also, if it were the driver's side 02, there used to be a big problem with the wires chaffing against a wiring clip on the back side of the engine block. It would ground out the sensor wire. Ohming the wire would show good continuity, but again... the signal was being grounded out.