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Discussion Starter #1
This is for my 1999 4.6 Bosch P38.

I’ve had this problem for quite some time. Since Feb 1 actually, when I had a u-joint fall apart on the front driveshaft. The flailing around of the driveshaft ripped thru the wiring on the left, post-cat, O2 sensor. It was the wires that are part of the sensor itself not so much the wiring that is part of the vehicle wiring harness. I did have to replace the connector that is part of the harness along with the sensor itself.
What I keep getting is code P0140, no activity from bank1 sensor2. I have replaced the sensor with Bosch replacement sensor, twice.
My scan tool reads live data and it says the voltage for this sensor is a constant 0.445 volts, no fluctuation like the other 3 sensors.

I have, as best as I can, physically examined the wiring and can’t find anything wrong. I removed the ECM and all the plugs on it, located the the 2 leads that go to that sensor and checked for continuity with an ohm meter and they test fine. There doesn’t appear to be a short between them either as I had no continuity when crossing up the test leads.

With the ECM and all the connectors back in place, with the ignition key on ( Pos2), and no sensor attached, I only get a reading of 0.445 volts on the wire that if I read RAVE correctly should be the 5 volt reference feed.

So does this mean my ECM is bad.
Any other ideas. July was state inspection month for me and it won't pass as it is now.

Thanks
Dave
 

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Seeing the reference voltage there all the time is normal if a sensor isn't working for any reason. You mention 2 wires going to the sensor but there should be 4, 12V and earth for the heater and signal + and -. Can you extend (or unclip) the wiring so you can swap over and see if the fault stays with the same sensor (just in case you've been really unlucky and got a bad one) or moves to the other side. Unlikely the ECM is bad as it is putting out the reference voltage.
 

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Discussion Starter #3
The 2 wires I checked for continuity were the signal and ground leads, the two leads that are shielded as they go to the sensor. I didn't check the wires for the heater as a fault there would have given me a different code but I guess I should check there as well. I know a bad ECM is probably rare but I don't what else it could be. I have try two different brand new Bosch sensors.
And yes I have a reference voltage at the ECM but it's only .445 volts. Isn't it supposed to be 5 volts?
Thanks for the reply
 

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No, it's supposed to be half of the lambda sensor output so that when running in open loop the ECM doesn't adjust the short term fuel trims so they are way out. As you have standard Zirconia sensors on a Thor engine they will show 0.1V for a weak mixture and 0.9V for rich, so 0.445V is absolutely correct. Without a heater supply, you will get no output from a lambda sensor, especially not a post cat sensor which will run much cooler than the pre-cat sensors. A pre-cat sensor will give an output with no heater connected but only when running under load, not when idling as it doesn't get hot enough, a post-cat never will get hot enough.
 

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Discussion Starter #5
I'll get the heater wires checked this afternoon. I'll let you know what I find. Thanks.
At least I'm learning as I go.
 

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Discussion Starter #6
So, what I found so far is, according to RAVE one of the wires for the heater circuit goes directly to the fuse box. The other to pin 7 on the ECM connector dedicated to the O2 sensors. With the sensor unplugged and the ignition key on I checked for voltage on the appropriate wire and found 12 volts. Then for kicks I checked the other wire and found 12 volts also. That seems odd to me. So with the key off now I checked with an ohmmeter and found continuity, no resistance, between the 2 wires, with the sensor still unplugged. It would seem to me then that I have a short in the harness between those 2 wires. I wouldn't get a code P0141 because the ECM sees the voltage coming back to it and can't tell that it didn't go thru the heater. The current chooses the path of least resistance and avoids the heater element. Am I on the right track? Tearing deeper into the harness doesn't look like fun.

Thanks
Dave
 

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That seems reasonable. Perhaps part of the loom has been mashed further up? I can't check RAVE right now but do make sure the two heater elements aren't paralleled up because that would give you much the same effect.
 

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Pin 7 gives a PWM output of between 12 and 0V so pulses the heater (the other side being a 12V supply direct from the fusebox). Pin 1 on the same connector operates the RH post-cat sensor so you should be able to compare what you see on pin 1 with what you see on pin 7. I'm with Gordon on this that the loom has got mashed further up, possibly where it goes through a clip?
 

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Discussion Starter #9
That's a good point. I do think they are in parallel. Before I replaced the bad connector I did get a heater circuit code for both rear sensors as a result of the one connector failure. When it failed the sensor was essentially unplugged. I'll unplug the other rear sensor and check again.
 

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Discussion Starter #10
I feel like I'm back to square one. With the other rear O2 sensor unplugged I no longer have continuity between the two heater wires which makes sense now, but it suggests that there is no short. I'll do some more testing at the ECM.

Thanks for all your help.
 

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The two sensor circuits are totally separate. They both have a 12V supply from fuse 26 in the engine compartment fusebox on a Brown/Pink wire. The LH sensor then has a White/Blue wire to Pin 7 at the ECU while the RH sensor has a White/Blue wire back to pin 1 at the ECU. So unplugging one should have no affect at all on the other.

Signal and ground for the LH sensor goes back to the ECU on pins 17 and 11, while signal and ground for the RH sensor go back to pins 14 and 8. The signal and signal ground wires are screened and both screens are connected together and then earthed at a common point. That is the only common connection between the two sensors
 

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Discussion Starter #12
I'm still battling this problem. This is the first chance I've had to spend much time on it for weeks. I have a donor vehicle so I removed the wiring harness from it, right from the ECM down to every sensor on the engine, completely removing it from the vehicle. Then I carefully opened the loom up and removed the O2 sensor connector and all 4 wires. The only wire I had to cut was the 12V feed for the heater circuit as it is spliced in. The other three wires I released from their homes on the ECM. I spliced the heater feed into my wiring just below the factory spice. The other three leads plugged into the connector on the ECM. I was pretty proud of myself until I started it up, let it get warm, and found out I have the exact same problem as before. 3 sensors working fine but no activity on that O2 sensor, bank1 sensor2. Replacing the wires didn't help at all. Tomorrow I will swap the O2 sensors from one side to the other and see if the problem follows it. I doubt it because I have already tried two different new Bosch sensors and have the same problem but I'll give it a shot. Maybe I will swap the wires on the ECM, putting bank 1 wires where bank 2 belongs and vice versa. If the problem goes to the other side would that tell me the ECM is bad?

Thanks for reading
Frustrated owner
 

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1995-2002 Range Rover P38A
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I'm still battling this problem. This is the first chance I've had to spend much time on it for weeks. I have a donor vehicle so I removed the wiring harness from it, right from the ECM down to every sensor on the engine, completely removing it from the vehicle. Then I carefully opened the loom up and removed the O2 sensor connector and all 4 wires. The only wire I had to cut was the 12V feed for the heater circuit as it is spliced in. The other three wires I released from their homes on the ECM. I spliced the heater feed into my wiring just below the factory spice. The other three leads plugged into the connector on the ECM. I was pretty proud of myself until I started it up, let it get warm, and found out I have the exact same problem as before. 3 sensors working fine but no activity on that O2 sensor, bank1 sensor2. Replacing the wires didn't help at all. Tomorrow I will swap the O2 sensors from one side to the other and see if the problem follows it. I doubt it because I have already tried two different new Bosch sensors and have the same problem but I'll give it a shot. Maybe I will swap the wires on the ECM, putting bank 1 wires where bank 2 belongs and vice versa. If the problem goes to the other side would that tell me the ECM is bad?

Thanks for reading
Frustrated owner
You logic is sound to me, and if the sensor shows up as being OK when you swap them over, and also the wiring shows as ok when you swap the pins at the ECU, then the only other common denominator is the ECU.

I guess it is possible that one of the circuits in the ECU was shorted and damaged when the wiring loom was originally hit by the prop shaft...
 

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Discussion Starter #14
Ok, so here's what I did tonight. Bear with me, I get myself all turned around trying to keep the numbers straight so if you can't follow me it might be may fault.

I was going to swap the sensors from left to right and right to left but the right side, which is working, is pretty rusty and didn't want to come right out with a wrench so I didn't fight with it. So I turned my attention to the ECM. First I swapped the sensor heater output drive wires L-R and R-L, pins 7 and 1 in the connector. I started the engine and after warming up there was no change in the sensors. Bank 2 was working but bank 1 was not, steady 0.445 volts. That tells me the ECM heater control circuit is working (which confirms my voltmeter readings).

So leaving them there I then switch over the remaining wires, ground signal and input signal, for both rear sensors. Pins 11 and 8, and pins 17 and 14. Started the engine and live data on my scanner continued to say bank 1 was not working but bank 2 was. So actually the wiring and the sensor on bank 1 were working but the ECU thought it was looking at bank 2. Evidently one, or both, of the 2 pins, 11 or 17, for bank 1 sensor 2 is not functioning.
So where does that leave me? Sounds like it must be the ECM or am I missing something. I hope so.

Thanks
Dave
 

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Discussion Starter #15
I guess it is possible that one of the circuits in the ECU was shorted and damaged when the wiring loom was originally hit by the prop shaft...[/QUOTE]

Thanks Marty, I was thinking that maybe the 12V heater circuit got fed into ECM thru one of the signal wires.
 

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That would be my best guess to be honest - if you are getting 0.445V measured with a multimeter, then it sounds like the feed is ok, but the return wire to the ECU would probably not like 12V being shoved up it, as it is expecting between 0.1 and 0.9V as previously mentioned. So 12V (over 10x the expected voltage) on a sensitive circuit like that would probably kill it to be fair.

I can't remember if 0.445V is the default reading for the voltages that displays even if a sensor is unplugged or not... I seem to remember that my Nanocom shows that the downstream O2 sensors on my vehicle (which aren't even fitted in the UK market) are reading 0.44V all the time - so it could be that the reading you are getting is the 'default' value, but it is throwing the error, because it is expecting that value to be changing and it's not. Which would point to the fact that something in the ECU is damaged, yes.

If you can get a replacement ECU, you should be able to just get it synced up to the vehicle, reset the adaptive values (so it clears any adaptation from the vehicle it was in) and then be on your way again.

If that STILL doesn't work, then there are obviously some really mystic forces at work, and I would advise an exorcism....

Seriously though - the ECU seems to be the ONLY thing left in the chain that hasn't been changed so far, and as nothing else has made a difference, I think it is the only realistic possibility left... and definitely not a normal failure item... but then you didn't have normal failure conditions either I suppose...
 

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Discussion Starter #17
I could start another thread but since I'm here......
What type of equipment does one need to sync a replacement ECU. I read that it doesn't have to be LR dealer but does it have to be a Rover specific tool?

And Does the Replacement ECU have to be the same year vehicle and have the same Bosch Number on it?

Dave
 

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There are only 2 part numbers listed for NAS spec P38s from Vin XA410482 (start of Bosch models)

Part number NNN100660 is listed for vehicles without SAI, and part number NNN100600 is listed for vehicles WITH SAI.

I don't know what Bosch part numbers they relate to, but a bit of a Google search might turn up a cross reference.

Synching the ECU can be done with various diagnostic tools these days, faultmate, nanocom, lynx, hawkeye, to name a few of the popular home user units. You can also get a syncmate which will do it, but I feel they are very expensive for the fact they do one job only, for just under half the cost of a whole nanocom ( at least here in the UK).

Other diagnostics such as rovacom, testbook, autologic etc can also do it, and there are a few others or there which have had input from omitec ( who originally made testbook for LR) which I would expect to be able to do things like a resync

Marty

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Discussion Starter #19
Thanks for the info Marty. I have a spare ECU but the rig has SAI. I will buy a used ECU for my truck and get someone local to sync it in.

Dave
 

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Discussion Starter #20
My hopefully last post in this thread. I got a used ECU from Will Tillery and a syncmate from BBS and the problem has been fixed. After starting the truck I hooked up my scanner and verified that I have signals from all 4 O2 sensors.

So, if anyone needs a syncmate for Bosch P38 let me know.

Thanks for all the help
Dave
 
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