Hey everyone,
I've been going through things trying to diagnose an oxygen sensor code (P0154) and am wondering if the ECU got fried somehow.
Questions are, A) can a bad ECU affect only the single O2 sensor? and B) If I test the resistance of the two pins in the ECU where the O2 signal & the O2 signal ground feed into it, should it read as a continuous circuit? If it should, I could test whether the wiring issue is within the ECU. I just don't know enough about circuit boards or ECU's and how they operate.
The only reasons I suspect it are that I have swapped in two other O2 sensors, which both work on the driver side but neither or the original work on the passenger side. I've also tested continuity of all four wires at the harness connection. Heater wires are continuous, signal and signal ground wires aren't continuous at the pins in the connector, but they are each individually continuous from O2 sensor connector to the connector pins at the ECU. Which to me leaves either the ECU, or I am barking up the wrong tree entirely.

 

Hi. An oxygen sensor error code does not imply the sensor is bad. All the connectors, wiring, terminals, splices end to end are also subject of suspicion.

"Reading a continuous circuit" seems you are measuring continuity or resistance. That is not the best of measuring methods. The sensor itself outputs around 0.5V when heated and engine exhaust is proper and such signal must be fed and present all the way into the ECU. Better read the voltage for diagnosing that. For the heating circuit, should read about 13V and fed all the way into the sensor healthy guts when heating is active.

 

Hi Externet, thanks for the reply. Yes, I was measuring resistance. Would I start by disconnecting the sensor from the harness and read the voltage from the sensor while the vehicle is running then? And then reconnect and read at different points along the wire? For the heater would I just wait until I can start the vehicle cold and then measure at the harness connector?
BTW my ultraguage is giving a reading around .45 volts, with very slight variation, but it is constant instead of alternating between .1-.8 volts like the other sensor.

Thanks for your help.

 

I had a bad ECU and it affected only the left upstream sensor.

When I got the D2 it was throwing the code for that sensor. While changing out the O2 sensor I have mistakenly broken some of the wires off at the connection on the wiring harness. After struggling to repair the connection and still getting the code I replaced the entire engine wiring harness but I still got the code. At this time I swapped out O2 sensors but still no luck. As soon as a got a new ECU with a paired BCU everything worked fine and I started getting the correct live readings on my ODBII reader.

It had this issue when I got the D2 and I did not know the history of the vehicle so I'm not sure how the ECU went bad.

 

Keninnc, that certainly reassures me that it's at least a possibility! Did you have any trouble installing the new set, and did you also have to install a new instrument cluster? Also, did you have SAI? The issue started after I was doing some other work on that side of the engine (right side) so I thought maybe I snagged the wire against the exhaust and fried something, the only thing is there's no visible melting or anything.

 

Has anyone ever pried the lid off their ECU and tried to visibly check if a component has broken?

 

I think so. The lid is screwed on so no prying needed. I have seen pictures of them opened up with water and rust damage.

 

I had water and corrosion in my ECU. I don’t know if you need to also replace the BCU to match, but that’s what we did (both from the same vehicle at a wrecker).

 

There are a couple of issue to know about that I had to learned when putting in a new ECU.

First off, it is very easy compared to getting under the engine and swapping O2 sensors. Basically remove the glove compartment and the trim piece that is to the right of it by the footwell. The ECU is attached to the body behind this trim. I remember 5 plugs to unplug and plug back it. The BCU is behind the glove box. Again about 5 plugs to plug and replug. It's kinda of a tight fit.

It is easiest to find a matching pair of ECU and BCU. The Nancom is supposed to be able to synch them but I did not have luck when using my Nanocom. Since then Blackbox Solutions has upgraded the software.

The BCU and the instrument cluster both keep the milage. So if they don't match the instrument cluster will blink the milage. If you have a Nanocom you can turn off the blinking. The replacement BCU will have a different milage since it came from a different D2 but it really does not matter. Again the Nanocom is supposed to be able to synch the instrument cluster with the new software but I did not have the new software at the time when I did this.

The other thing to know is the interior fuze box synchs with the BCU. If you plug everything in and try to start the engine it will be immobilized and the red light on the instrument panel will be on.

The BCU synchs by putting the key into the II position and leaving it there for 5-10 minutes. When the red light goes off you know it is synced and you can start the engine.

If you think it is the ECU then my suggestion is by a synched pair and use a Nanocom to turn off the blinking. The Nanocom can also re-synch your key fobs.

Yes I have SAI

I have removed the cover from an ECU. Since I don't have any electronic training or have any real electronic diagnostic equipment it really does no good. Just one big circuit board that I have no idea what everything does.

 

Just got done fighting this myself turns out the O2 sensor pins in the ECU connector were loose. Everything is fixed when I backprobed the connector to get readings on my Oscope.
https://landroverforums.com/forum/di...-loose-104955/