Please help,

I have a 2002 Discovery SE7 w/4.0 (secondary air) and an automatic. There's a 124,999 miles on the odometer, Here's my problem. For some reasons I continuously get 02 Codes, P0135, 155, 150, 130 and now (new) P0139 I changed the sensors multiple times (no go) change out the ECU wiring harness (no go) and finally sent out the ECU for reprogramming/upgrade $$$ and the same codes. This morning I decided to do a smoke test and there were no negative results for vacuum leaks. The car runs well and is in good shape for a 19 years old but, just wont smog. Oh yes it's in California. Am I missing something?

 

Based on your codes, you are all over the map in terms of the O2's. I am dealing with the codes that indicate no voltage going to O2's. Popped up after and HG job on drivers side, and then after splicing in a new DS connector, on both sides. I have tried to nail down but finally gave up and took it to a LR independent guy. first thing he said was did you check ALL the fuses? I responded with just the ones related to the O2's. Clearly this is electrical. Was the harness you installed new or used? If used you may have problem there. Did the codes all start popping at once or did they continue to pile up? What kind of O2 sensors are you using? What grade gasoline? I ask about the gas because your new code is for the post cat O2. Everything else is pre-cat.

 

Thank you for your response,

These codes were always the problem since I bought it almost 5 years ago. I never actually drove the car much just test runs and it was (still is) a project and garage kept. The wiring harness was used and was from a Secondary Air motor too. There were no noted breaks in the harness. Nevertheless after the harness was replaced the same codes would reappear. I don't recall the brand of the 02 sensors but, they were purchased from Lucky8 which specializes in Rovers. I understand that Bosch are the premium to purchase but I don't want to spend $$$ only to find out there not the problem. I use union 76 fuel and it is the 91 octane in California. I understand that some Union 76 stations offer racing fuel with a higher octane for $10/gallon but I have my reservations using that on a rover engine just to clean it out. I suppose I overlooked the fuses to. Which ones are you referring to?

 

You should check every single fuse in the car: both in the box in the car and the one under the steering wheel. F2(in engine compartment) is the one that is designated for the O2's. I would check every single one you can remove and inspect. Can't hurt. but Bosch O2's were the OEM part. I had purchased several from AMZN and they were bad. I switched over to Walker which I purchased from Atlantic British. They were good out of the box and no issues for a very long time. when you sat there were no noted breaks, you stripped the wire loom off the whole thing?
Another suggestion I have is that you take a very hard look at the connectors at the end of the harness where they join the O2's. They are tiny pins which can get damaged easily. make sure there is no oil or grease and confirm the pins are properly seated. I did this when mine went sideways after my HG repair. You should also check the post cat O2 wire to see if might have melted.
I offer these observations with the caveat that I could not solve my issue. I finally had to take it to an independent Rover specialist. He thinks my issue may be in the splice I had to do to replace the damaged O2 plug on the DS side. Hopefully I will know soon.

 

I thought I should update you with a sitrep on my O2 codes. My mechanic called me and told me I had two problems: 1) That a splice in my harness going to O2's was not good. I am not sure if he was referring to the splice my buddy and I did or he found another further up that I did not know about. If it was not mine, it would be the only real work done that I have found and I have owned this car since 2011 and 55k miles. 2) My engine control module was shot. No the whole thing but the part that deals with the O2's. The ECM's are solid state so when they go they go. This thing may have been dicked up for a while as I have been tossing codes since last June. The car could not pass smog, but COVID kept the Registration good until Nov last year.
Given all the codes, you too may have an ECM issue as well. My mech said they do not go all the time but they go. You have 125k on your '04 and I have 174k on mine so perhaps the issue is one of age for both of us. Let me know how it turns out.

 

Hi Matt,

I spent some time with the car this morning and checked all the fuses and all were fine. I notice the front 02 brackets were removed from the bellhousing. (I found them under the hood on the shelf below the wipers) why were these removed? Do they act as a ground? In any event I unplugged both bank 1 and 2 upper 02 sensors and cleaned the plugs. Here's what was weird, I did get some voltage from both sensors (minute amount) but things went haywire from there. The engine began to run rough, the SES light was flashing and codes were showing multiple misfires on cylinder 4, 8, open loop error and one code even warned of Catalyst damage. So I shut the motor down and restarted which the problems disappeared but the 02 sensor codes reappeared (no volts). I'm looking for a needle in a hay stack. My engine computer was reprogrammed last week and installed but the same 02 codes appeared after. Please keep me posted. You have become my only savior with this problem Thank You.

 

Jumping on this thread so I can follow progress. I’ve been having codes pop up for MAF, O2 sensors, SAI etc. Rover mechanic quickly found that fuse 2 in the engine bay kept blowing. He spent half day looking at things but needs more time. Not sure if it will help your troubleshooting but I’ll share the results next time I can get back in.

 

The bracket do not act as grounds as the O2 plugs lock in there for a positioning point. There is only a small amount of voltage that runs thru to begin with, less than one volt. If you are using an Ultra Gauge, it will read "0.445" at start and move up and down. Was there a lot of crud inside the O2 plugs? The internals of the plugs them selves are pretty fragile, thin male female connectors with the bulk of the plastic plug to protect them. Clearly your disconnect and cleaning woke something up. In your initial message, and you most recent, you mention sending out your ECU to be reprogrammed and "upgrades". Just thinking out loud here, but I wonder if your " upgrade" is what is causing you problem. Did you have it reprogrammed once or twice? What area do yo live in? I do not know how a computer is reprogrammed in terms of where the connect to do the programming. Perhaps on reconnection of the plug group that deals with O2 something got messed up? I never messed with the computer myself. I conceded defeat and to it to a mechanic who is an LR specialist. I don't want to stomp your buzz or shatter your self confidence in terms of getting this fixed yourself, but unless you took those brackets off yourself it is obvious someone did and the PO mechanic may have been chasing what you are chasing now.
I am by no means whatsoever an expert on this. I am just passing on my experiences

 

Hi Matt,
I'm pretty much getting to the point where I need to take it to a rover specialist if I ever want it on the road. I had the computer rebuilt/refurbished with https://www.precisionecu.com. It has a 1 year warranty and they are very helpful with information. However there scratching there head on this one.
I'm confident with the ecu rebuild so it comes down to a wire(s) I may have pinched, broke or striped something when I put things back together. It just a coincidence there the same codes since day 1 when I bought it. What a mess. My worst case scenario would be closing the doors on it and it may someday become a barn find. I thank you for your time with correspondence and hope you get yours up and running soon

 

Good Morning- My buddies and I used to have a saying when we would get aboard a USMC helicopter ( after it had been delayed due to a mechanical issue) 100,000 moving parts, all made by the lowest bidder are expected to work with all the other parts made by the lowest bidders. I have come to think about LR's in pretty much the same way. If you are confident in the ECU, reprogramming, then I suspect you are right about the wiring harness. With all those connecting pins and the heat the engine harness is subjected to, it's very like that is where your issues lie.
My rover (aka Winston) is up and running. As I said, I conceded defeat when my buddy and I had exhausted our knowledge base, what ifs and his OCD when it comes to solving an automotive issue. My issue was twofold: despite our best effort, our splice into the wiring harness for the DS O2 sensor was just not good enough and my ECU had been performing poorly for a while, going back to August when I tried to pass inspection and could not due to emissions issues.
Keep us posted on how you make out. Everyone learns when members close the loop on resolved problems.
Good Luck!