Hi folks,

my bro just bought a 2003 STR with 120k miles. He bought it with a P0105 code (and nothing else) three months ago. We erased this code and it never came back.

Since he bought the car and we erased the P0105, 3 new codes has appeared: P1646 related to a faulty upper 02S, P0191 & P1339 related to the FPS and/or the fuel pump. We analyzed the streams and some values seems irrelevant:
- the car is running in open loop mode (both lines);
- both the upper oxygen sensors send a 0.999 lambda and 0 mA;
- both the lower oxygen sensors send nearly 0V;
- the fuel pressure is between 3.7 and 4.1 bars.

We erased these 3 new codes (and only the P1646 came back) but the car continue to run in open loop mode. This is not surprising regarding the values given by the upper O2S.

Do you think the 4 O2S are dead ? Is-it possible to have them dead in only 3 months ?

Thanks,

Laurent

 

OL will cause cat damage if allowed to go on for long (not to mention poor MPG).

P1646 is just one sensor - I'd replace it before doing much else.

 

you're right, P1646 is juste one sensor.

But how do you explain the values returned by the others sensors ? The upper O2S are supposed to go up and down every 1s but they return always the same values. Same question for the lower O2S which are stuck to 0V. Are these sensors working well ?

Laurent

 

It may be unable to use the sensors or there's something else wrong but with a known fault with an easy fix I'd start there.

An alternative is to follow the workshop manual for each fault, hoping to find something - probably it's a better idea but it will take a long time I suspect and you can always go that way if nothing gets better having changed the one O2 sensor.

Obviously, make sure to use a proper replacement and to change the right one (sadly, people before you have fallen foul of both these obvious points!).

 

Got it. Thank you JagV8.

Laurnet

 

IIRC, 2003 and later models used wideband O2 sensors. These have a variable "sliding" output, not the simple high/low output found on earlier models. The old style could only tell you if the exhaust was rich or lean, but now how much. Wideband sensors don't switch back and forth at the sweet spot like older sensors. They just put out a variable signal directly proportional to the oxygen content. It could very well be the upstream sensors are accurately reporting a rich mixture.

Same with the downstream sensors. Their primary purpose is to monitor catalyst efficiency. (They also help fine tune fuel trims) If the cats are cleaning up the dirty exhaust, the value they are reporting may also be accurate.

I'm surprised you're not getting some fault codes related to the control system staying in open loop. Have you driven the car much with the current fault codes? If there is such a fault code for staying in open loop, it may require more than one or two drive cycles to set, I'm not sure.

As JagV8 has suggested, take care of the known faults first and then go from there.

Edit: Forgot to mention, OBD codes are here:

http://www.jagrepair.com/images/Auto..._OBD_II_R2.pdf


Much more info here:

http://www.jagrepair.com/JaguarSType...OBDIIcodes.htm

 

Wideband aka linear etc - use current not voltage to sense.