Recently I encountered a problem with my 2002 XJR. I got a CEL and when I checked the codes it was P1646 and P1000. I assume the P1000 is due to the P1646. I only get the CEL, not restricted performance. When I reset the codes and start the engine again, everything works normally. I drive a bit, stop, shut down the engine, wait for a few minutes. When I start the engine again the CEL pops up with the same two codes again and never restricted performance. I have tried this 5-6 times and it happens every single time. Car drives fines otherwise, with and without the CEL/code. No loss of performance at all.

My VIN number is F50404, so on my car as far as I can tell the P1646 is related to the fuel pump relay 2 malfunctioning. (and not the O2 sensor as on earlier models for this P-code)

I have checked the voltage to the relay which is fine. I have jumpered the relais and put 12V directly onto the fuel pump. When I do, I can hear the pump and can hear fuel inside the tank sloshing around. I have swapped relays and checked all relevant fuses.

I can't get into my Jaguar 2002 workshop manual. I have an old Jaguar Heritage digital, encrypted, manual. Won't work anymore. So I am going to find myself a new 2002 workshop manual. I am pretty sure there are several tests described. (I have a 1998 manual, but the test described in the 98 manual doesn't work as they refer to other connectors)

also have the XJ series Sedan 2001/2002 electrical guide. Strangely, the wiring on the ECM connectors is different (colourwise) than what the diagrams show. I am a bit reluctant to start continuity measurements with a multimeter unless I am one hundred percent sure I am measuring at the correct pins.

main is that this looks like an intermittent problem that occurs only for a few seconds, enough to trigger the CEL/P1646.

Any thoughts/suggestion what this could be or what else to check?

Thanks

Jeroen

 

P1000 is because the codes have been erased and the emission monitors have NOT been reset...yet. So you won't be able to get your car thru a smog check until they complete. You can tell this as that P1000 will turn to a P1111. So it's not an error code just a status code.

Do you understand the monitors and how to reset them? As I posted above the P1000 did not pop back on. It never left because the car has not completed the monitors yet.

I have seen this mentioned and it's confusing as you say because it's almost always pointing to an O2 sensor.
I do have a suggestion? Since the SC cars use 2 pumps to feed the engine maybe remove the fuel pump relay number 1 and see if the car will run on just the second pump?

On the SC cars the second pump is usually brought on line from 3000 rpm and up. Does the car pull hard from 3000 rpm and up? I have seen people complain of a lack of power on an XJR at higher speeds.
You also could measure what your fuel pressure is doing?

But first take a look at this thread? Very interesting BUT not a SC car and an XK.
Sad too as he never came back so we don't know how or if he fixed it? Probably was an O2 sensor because it was a non-sc car.
XK P1646 Code

Attached is a service bulletin related to what you working on and may help? Note it covers both the XK and XJ. But those cars all had stalling problems which you don't have?
It talks about and has a troubleshooting flow diagram on fuel pump relays.

Here is another thread to test whether one or both of your fuel pumps are working. Real interesting!
XKR Fuel Pumps

My wild as guess is you need a secondary fuel pump.
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Thanks. Yes I am aware on what the P1000/P1111 means. It is just that the P1000 keeps popping up in combination with the P1646. When I reset the codes they both disappear. I just mentioned it for completeness on what I see on my scanner.

I am not sure on how the second fuel pump logic works. I thought it only kicked in at higher RPMs, so with fuel pump 1 relay pulled, it might not start at all. I will give it a try. As I mentioned, when I jumper the relay I can hear pump 2 kicking in and fuel flowing in the tank. Whether that is with sufficient pressure and volume I don't know.

My XJR pulls fine, also at high RPM, so I have no indication that fuel pump 2 is not working. I still think this P1646 is just popping up without anything being amiss as such.

thanks for the interesting document. I will be taking a close look at it.

Jeroen

 

pull #2 relay out RP and the relevant DTC should come on right away, the relay coil is always monitored.

you can hear #2 prime when you cycle the key to position 2. no #2 pump = no fuel prime on an sc car

 

Thanks, did that, when I pull rely 2 I get P1646.
pump is running, but I still get this blasted code. Every second time I start the engine after codes have been reset.
Jeroen

 

still no RP?

verify power side feed of relay coil is good. if yes run an overlay from ecm ground control pin all the way to the trunk. no change replace the ecm

 

No RP. I will try to run that cable see what happens. But I don't have a spare ECM. As far as I know that also requires programming, for which I don't have the equipment either. I will figure out some more tests in the next couple of days.

Jeroen

 

How about replacing the relay? What if the coil resistance goes off when it get's warm? How about the relaybox itself?. Whati if that has broken solder joints (would not be the first Ford this type box that has broken solder joints.)?

 

I was perplexed when P1646 was being talked about as an 02 sensor then a FP relay. I have only known P1646 as an upstream 02 sensor on bank 1. Fortunately for you that’s the easy side. I did search for an 02 XJ code book on Gus’s website below and I noticed the discrepancy. If you look at the 99’ XJ code book (still an AJ27 engine like yours) link, you can clearly see that it’s for the 02 sensor and not a FP relay. Not sure what went wrong for the 02’ XJ code book… anyways… If you disconnect the upstream 02 sensor on the passenger side and using an ohm meter, you’ll likely find the 2 black wires for the heater circuit within that sensor to be open. I can assure you that this is the correct path to take to resolve your issue.

http://jagrepair.com/images/AutoRepa...J27%201999.pdf

 

See my first post. Swapping the relay was just about the first thing I did!
It could be in the relaybox itself. The X308 was a complete inhouse development by Jaguar and you would be hard-pressed to find any Ford parts on it. (The electrical chair controls are the only one I have come across). All other electronics is Denzo it appears. Mind you, when it comes to iffy-quality Jaguar can give Ford a run for its money of course

Sorry that link wont work for me. I have lots of technical documentation showing that on later Supercharged models P1646 is related to the secondary Fuel relay and not the O2 sensor.


But I am going to test the O2 sensor just in case.

There are also several threads on this forum confirming the same:
E.g. https://www.jaguarforums.com/forum/x...01-xjr-261844/

Jeroen

 

I have run across that code and it was a faulty O2 sensor.

 

Randy, was that on your 03’ XJ8 that you’re speaking of, or your previous 98’?

 

Peculiar P1646 problem

Reminds me of the scene in ONE FLEW OVER THE CUCKOO'S NEST

https://getyarn.io/yarn-clip/480c79e...2-1c8c758d5818

 

Jaguar AJ27 "DTC Summaries – EOBD" (European OBD), for 2001 ON, also show that P1646 is for the Pump 2 Relay so it is not a typing error in the "OBD II" tables.

 

One of the links I posted above had a procedure for running the car on just fuel pump 2?
Have you attempted that? What were the results? Both pumps working?
Testing Thread;
Fuel Pump Tests

After much research it's just very confusing all the way around? Why would Jaguar take a known O2 error code P1646 and then use it on a completely unrelated problem concerning fuel pumps? Also note the fuel pump code definition is ONLY for the 2000-2002 XJR/XKR cars (at least from what I can find). On any other car it means the O2 sensor.
Very strange decision by Jaguar on this one.

Since the car seems to be running fine is there anything to fix?
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THE PLOT THICKENS!!!

Thanks for everybody's comments and suggestions.

Based on all the formal Jaguar documentation I have in my possession and that has been presented to me in this and other Jaguar forums, there can be no doubt that my 2002 XJR P1646 constitutes a problem with the secondary fuel pump. In accordance with said official Jaguar manual I have performed all test as suggested, and some more. But I could not find anything wrong!!

As I mentioned earlier, when I reset the codes, the car will fire up fine and drives fine. When I pull the secondary fuel pump relays the code P1646 pops up immediately.

So this morning I put my Autel scanner of live data and drove around a bit, observing some actual live data from various sensors.

Here you can see clearly, engine running normal, cruising, the secondary pump is inactive. As it should



Next I used the graphic function and gave my Jag the beans, and floored the throttle. You can see the secondary fuel pump kicking in for a couple of seconds. I also timed my acceleration. About five seconds to power right through 100 km/h. Nothing wrong here with the performance!



Next, I pulled the relais, got the CEL and the code and redid these tests. Even with the CEL on and the code P1646 present the secondary pump still kicks in.
I also looked at all the live data of the Lamba sensors. I can't find any differences between right and left bank. I am getting near identical readings on all measurements.

So time to call in the experts. I live in the Netherlands and we have a real X300/X308 specialist here, a chap known as Raymond. He and his wife Joke run G&G Autoservices. All he does is work on X300/X308. There is little that he has not done, seen or tried.

Raymond was adamant that it was the Lamba sensor. Sure enough, when I checked the resistance of the heater I measured infinite! Managed to get the sensor out and Raymond is looking for a new one. There are many variants about.

Fingers crossed he has one in stock.

I find it quick baffling on what it written in the official Jaguar workshop manuals is so different from how these cars seems to work. Raymond never goes by the codes. He has the official Jaguar diagnostic kit and he swears by what it tells him. He also told me he replaces at least 40-45 of these sensors a year.

I will wait for me new sensor and report back what the results are.

Jeroen

 

That code came up on the 2003 and was a dead O2 sensor.

 

According to the DTC Summaries for 2001 ON, P1646 does not mean O2 sensor for NA engines. Codes P1646 & P1647 which were previously for the O2 sensors (banks A & B upstream) were replaced by codes P3007 & P3008 for NA (and also for SC) engines. Could it be wrong?

 

Thats peculiar. According to my code reader and autocodes.com, P1646 and P1647
are related to the O2 sensors.

 

Gents, I am very happy to report my P1646 has been solved! thanks for all the suggestions and comments.

As I mentioned in my last post, I spoke to Raymond of G&G Autoservice here in the Netherlands. Little he does not know about X308s. He fixes them all day, that is all he does.

So he send me a new O2 sensor. It arrived and I installed it right away. I am very happy to report I have no more CEL and or error codes!!

So whilst I am very happy this problem has been solved I am still a bit curious as to what is happening here. As shown in various posts, there is plenty of official Jaguar documentation showing that for a 2002 XJR ( A27 SC) the P1646 means a problem with the secondary fuel pump.

What I am wondering is whether the documentation we are using/referring to, was updated at a later date. Lets face it, I have yet to see a dedicated workshop manual for a 2002 XJR. Most folks refer/use the 1998-2001 version. Freely available via various channels. Even Jaguar Heritage will tell you it is the correct manual.

When quoting from manuals or technical publications it would probably be an idea to not only mention the source, but also the date/revision level?

It is also a fact that when I pull the respective relay, I get a P1646 code!! Even so, replacing the sensor solved the problem. The old sensor heater had an infinite resistance, the new one I measured about 2 ohms, So there is no doubt in my mind that the old sensor was broken. What I don't understand is I get P1646 when I pull a relay for a secondary fuel pump! Following the Jaguar documentation too!

A bit baffling. It probably does show the difference between me being a hobby mechanic and Raymond doing this stuff for a living for the last couple of decades.

Jeroen