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Discussion Starter · #1 ·
so after doing headgaskets on a disco 2 i came up with an o2 codes no activity, signal implausible. b1 s1. i found the connector to be a problem a long with the wiring harness. i was showing 1.125v KOEO. Ran new wires to the pcm for both the signal and ground also changed the connector. my voltage now sits at .45v. perfect, hook everything back up. Bank 2 starts switching, bank 1 stays constant at .45v. runs like **** get a heater code. run new heater signal wire to pcm. and swap Bank 2 Sensor 1 to Bank 1 because i know its working fine. still get no switching. I'm at a loss and need some help.any suggestions will be appreciated
 

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Discussion Starter · #3 ·
tracing wires back and following the a wiring diagram shows that these wires only control the o2s. the only wire that is used by mutiple sensors is the heater crkt from fuse 2. which is good.
 

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The O² sensor being stuck at .45V suggests a wiring problem because it's the center of the operating range. Not sure if that's the case in a Disco but the ground wire on an O² sensor is independent from the frame ground. I'd make sure that there is no short between ground and the sensor ground.

I replaced a connector on an old O² sensor for testing, and it's working fine. Did you solder the splice or did you crimp the wires?

0² sensors are funny animals. I had one that went to zero volts after running on the road for 10 minutes, but worked fine at idle in my garage for a long time.

If I was troubled with such a problem I'd order a new sensor to rule that part out. If the wiring is OK and the O² sensor is good, then it's the ECM, because it's actually the ECM that switches the voltage, not the O² sensor.
 

· '03 Disco SE
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O2 sensors operate using minute changes in voltage - even the most minor wiring flaw could throw it out of whack. When were the O2's last replaced? Are they OEM Bosch or some other unit?

I'm not entirely sure that the sensors are your problem though. It sounds more like a vacuum leak or leaky injector. I'm leaking toward vacuum because it's common to overlook a vacuum line or gasket when reassembling after HG replacements. Double and triple check that you have no leaks. Smoke test if necessary.
 

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tracing wires back and following the a wiring diagram shows that these wires only control the o2s. the only wire that is used by mutiple sensors is the heater crkt from fuse 2. which is good.
I do not mean that the wires are used by other items on the vehicle. Some O2 sensors need something to compare the the exhaust gas to. That is they need a clean air supply. They use one of the wires to obtain that reference air. Use the wrong wiring and it will not work.
 

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The O² sensor being stuck at .45V suggests a wiring problem because it's the center of the operating range. Not sure if that's the case in a Disco but the ground wire on an O² sensor is independent from the frame ground. I'd make sure that there is no short between ground and the sensor ground.

I replaced a connector on an old O² sensor for testing, and it's working fine. Did you solder the splice or did you crimp the wires?

0² sensors are funny animals. I had one that went to zero volts after running on the road for 10 minutes, but worked fine at idle in my garage for a long time.

If I was troubled with such a problem I'd order a new sensor to rule that part out. If the wiring is OK and the O² sensor is good, then it's the ECM, because it's actually the ECM that switches the voltage, not the O² sensor.
Having O² voltage drop to 0v is the normal operation when responding to a out of normal operating condition. The control module ignores the O² in open loop condition. If it tries to go close loop or is in closed loop and the O² range exceeds a determined threshold the sensor is switched off and the system goes back open loop.

Likely in your case at idle all conditions were OK at low RPM's or idle. Once you raised the RPM's for normal driving something caused the O² levels to exceed the threshold in response to an issue like (vacuum leak, flat cam, leaky injector..etc)
 

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Having O² voltage drop to 0v is the normal operation when responding to a out of normal operating condition. The control module ignores the O² in open loop condition. If it tries to go close loop or is in closed loop and the O² range exceeds a determined threshold the sensor is switched off and the system goes back open loop.

Likely in your case at idle all conditions were OK at low RPM's or idle. Once you raised the RPM's for normal driving something caused the O² levels to exceed the threshold in response to an issue like (vacuum leak, flat cam, leaky injector..etc)
Ah that makes sense, thanks for that explanation. Prior to that problem I had a small vacuum leak and it was a dried out hose that caused it. I may have replaced it at the same time, which would explain my confusion.

Even then, I don't need much to get confused...:D
 

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Discussion Starter · #9 ·
i used a new bosh sensor as well as switch the banks. the wiring was crimped but checking resistance i have .5 ohm from pcm to connector. and anything under 1Mohm is acceptable. ive smoke tested it already found the valley gasket leaking. cinched the bolt down no more leak. this was prior to re wiring the o2.
 

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Discussion Starter · #10 ·
Fixed the problem. The bad PCM. The ground side driver is bad. Grounding the wire while still connected to the pcm allows the sensor to start switching. What a freaking pain in my ass.
 
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