I'm going to confuse things even more.
Steve XJR reckons that the ECM stops once it finds an 02 sensor code.
If you have a bad Bank 1 sensor then disconnecting Bank 2 will make no difference since it will set a 1646 and give up - in other words not see the second bad bank.
I'd guess that swapping the connectors and clearing the codes should work - Bank2 sensor(good) is now connected to ECM Bank1 so no 1646 but the 'bad' sensor is now connected to Bank 2 so should give a 1647.

 

Just to add to the knowledge base here.......

Got a 2000 XJ8 today showing a P1647 fault. Diagnosis traced it to an open circuit in the heater portion of the Bank 2 upstream sensor. So it's confirmed that is one failure mode that will set this fault. I believe an open or ground in the sensor circuit itself will also set this fault. I haven't been able to prove that as yet.

Baby steps........

Cheers,

 

Steve
Have you got time to swap the plugs and see if the fault code moves?
In the past people have been physically swapping O2 sensors but this approach is much easier.

 

I can tell you that in this case, swapping the connectors WILL cause the fault to change to the other side. That's because the failure is an outright open circuit. Immediately at key on the ECM can tell the circuit is open and sets the fault; and a clear and re-read will also show the fault sets immediately.

But as a diagnostic strategy, moving connectors is not a good one. Were this a PERFORMANCE FAULT, meaning the car had to be run for a while so the component monitor can run and test things, trouble would ensue. In that case, the ECM will be making fueling decisions for one bank based on what was sensed in the OTHER BANK. The engine will be running like crap in short order and you will have more problems than the P1646 or P1647. Believe me, I did this years ago as a test. It only took about 15 seconds before the engine would hardly run. Absolutely a terrible diagnostic strategy, especially if you still don't yet know the nature of the fault.

Edit: I should add that the test above was on a hot engine. If done on a cold engine, it would run somewhat longer, because then the O2 sensors are initially ignored as they are not up to temp for operation.

Cheers,

 

This would only be a problem when going into closed loop of course.
P1646 =
1. H2OS heater failure
2. H2OS sensing circuit short circuit to ground or high voltage
3. H2OS sensing circuit open circuit
so wouldn't all of these show up as soon as the car was started?

 

An update to my problem with P1646,
As i mentioned earlier I had the same error code and restricted performance flash up on my 2000 xkr.
I had the o2 sensor changed and the p1646 cleared BUT I had P0308 missfire on number 8 flag up (the other bank by the way), I tried the usual swapping plugs and coils all to no effect even a new set of plugs were fitted and still the same, It is sparking on that cylinder so appears to be a fueling problem, as I cannot get access at the moment to the injectors (intercooler in the way) I have not isolated the injector itself.
I tried autoenginuity scanner on it but it has confused me even more all my fuel trims give +ve and -ve readings and in fact bank 2(problem bank) it says it cannot read the trims as there is a fault, but it does not flag up with any codes so I do not know what the fault is,
So there I am at this moment in time, I still think it has something to do with the original bank 1 o2 sensor but why bank 2?
any ideas would be welcomed.
Thanks for now

 

Hi All,

On a 2000 to 2002 Jaguar XK8 none SC model, code P1646 and P1647 make reference to a failed or open heater element on the OS2 sensors. You can check this to verify with ease.
On US models, the 1647 is the driver side Pre Cat O2 Sensor, the 1646 is the passenger side Pre Cat O2 Sensor. The units are wide range units which are different to the O2 Sensors after the Cat.

To verify the heater unit. Locate the connectors (Grey) at the end of the pre Cat O2 sensor and disconnect the connection by pressing the tad press bar top release. When released, check the resistance in Ohms between the black wires. They should read 5 Ohms or thereabouts. If you get no reading, the heater has failed and this will generate the fault either P1646 or P1647. If both read 5 Ohms, check fuse #1 (30Amp) in the passenger side fuse box in front of the ECM unit. under the hood as this is the fuse for both O2 Pre Cat sensors. That may also trigger this fault.

 

Hi Steve,
P1646 or P1647 will show up after a couple of starts rather than the first start. The ECM checks the heaters as you drive. Not required, but they do and if the unit gets no feedback as an input to the ECM, then the flag is set.
Item 1. as you have mentioned is the case. Item 2 and 3 are alternate causes. They are related to wiring issues. IE A ground fault, high resistance in a connection etc.

Once the flag is set, the ECM no longer looks at the Pre Cat and sets the voltage to a nominal 4.5V for be used for short and long term trim values. So a failure, results in an average being used rather than dynamic feedback, slightly changing fuel consumption. The problem arises if you need to have an emissions test.....

Trust me, I have gone through this exercise before and worked it all out and checked every wire as both of mine went within a day of each other.

 

Hi all,

I've been reading this thread and the conflicting info has confused me, as with many other looking at the replies so far. I have a 2003 4.2L XKR, so the AJ34S engine with VIN ending A31718, done ~90k miles.

So from post #9:
And post #25:
BUT post #32 says:
MY car is also throwing up a P1111 code, which seem common when a P1646 is showing, but could be either "all tests passed ok" or could be an air temp fault.

I would welcome any advice before i start pulling out o2 sensors and checking wiring, or trying fuel pump relays etc.

Thanks in advance,
Richard

 

P1111 is Jaguar specific and means all test passed. It is not a fault code.

Your 2003 4.2L has only one fuel fump and P1646 refers to the O2 sensor fault.

 

many thanks for the info, I was under the impression all supercharged models had two fuel pumps but never having taken the tank apart on mine I've never looked. For my info could you clarify which model X's had two pumps, and which only had one?

Could I also clarify that the P1646 code is for the right hand upstream O2 sensor, and for my VIN (2003 4.2L SC) would be part number C2S51801 an that has the grey connector?

Cheers,
Richard

 

When Jaguar switched to the 4.2, (2002 in the UK, 2003 in the US), the design changed to a returnless fuel system with a single pump on both XK8s and XKRs.

RH upstream is correct but I do not have part number to confirm.

 

That statement is 100% correct.

WhiteXKR is also correct; to elaborate, a 4.0L SC has two fuel pumps, a 4.2L SC has one fuel pump.

Cheers,

 

And that is why it is so important to use the proper chart for your MY car!

 

Cheers everyone, will report back when I get the part delivered and I fit it hopefully next weekend. Gives me an excuse the finish of the camber adjustments too at the same time.

Cheers,
Rich

 

Hi all,

Just to report I received a new sensor today and swapped it, a 20 minute job of which 15 was spent wrestling the wires and connectors. Only a masochist would put them there on purpose.

Started the car, immediately got a "restricted performance" warning, orange light and engine warning light. I started and stopped it a couple of times, let it warm up (O2 heater) then cleared the codes and it seems fine now. I guess it was detecting a change in the load on that circuit until the ECU realised it was now the correct reading. Many thanks for everyones help. Cost me £120 for the sensor and delivery, but would have been twice that to take it to a garage.

For others' reference when I put a multimeter across the two black wires for the old one it was open circuit. On the new one it read 1.2 ohms, so the heater on the old one had packed up.

Cheers,
Rich

 

Hi All,

I too went through this issue trying to determine the codes. So here is the clarification.
P1646 is the left bank pre cat O2 sensor heater. Heater has failed.
P1647 is the right bank pre cat O2 sensor heater. Heather has failed.

In reality, these heaters come on periodically while driving to provide feed back. What they really do is heat up during the first 60 seconds after engine start to balance help control emissions.

So after the engine is warm, they serve no purpose, beyond a feed back loop and turning the light on on the dash.

If you have one of these faults, remove the connectors (Black if I recall, in any event, just follow one pre-cat wire to the connector to confirm) behind the center area on top of the transmission and switch the connectors with each other. If the fault changes from a P1646 to a P1647 then you have found the problem and validate the source.

You can also verify wiring and conductivity inside the ECM, but this will work every time.

Hope this helps,

Gord

 

Hi I have been reading the posts, and would like to ask a question on the same codes if anyone can help
I got 1646 code so changes Oxygen sensor on drivers side when finished started car up and got engine light which turned out to be 1647 which as I understand is the opposite sensor passenger side gray connector.
If i clear the code from the ECU theen the light goes out for a complete trip no matter how long as some as I turn engine off and then back on get 1647 code. Reading forum I read that sometimes can be relay fault? or do you guys just think its oxygen sensor bank 2 passenger side .
British car XK8 2003 4.2
Thanks for any help

 

Check F11 30A fuse in the Engine Management Fuse box. It is in the box with the Eng control module. You may have blown that fuse during the work. Was this a direct fit O2 sensor, or one you had to cut and transfer the connector??

Cheers,

 

Thanks Steve,
Yes had to change the plug, will check fuse.
I have bought a new sensor just in case. Not had the car long but the sensors came out without any fuss which makes me thing that they have been out before.