Hi Everyone, Went to a auction a couple of years ago to purchase a "sensible car" and came home with a wonderful 67K XJ8(wife is a Brit also). Been great then suddenly started the fail.-safe mode regularly. I cleaned the throttle body and that seems to have worked.
Suddenly the engine misfires, especially when cold. Checked codes and came up with P1111,P1642, P1647.
Problem is it seems every code list I look at is different. The first thing I addressed was a high pressure - fuel pump code. I changed fuel filter and it needed it. So far these codes show up at differently depending on where I look.
O2 sensor Bank 2 sensor 3
O2 sensor control chip
System pass
Air temp circuit range
Before I start changing out everything, any idea where to start.
Thanks
Ken

 

OK guys, need your help here. Disconnected battery during connection checks and now car is totally screwed. Lurching during acceleration, missing and really undrivable. Much worse when cold and when accelerating. Seems to do better after each shift when RPM is reduced then back to missing.
Codes 1111, 1642,1647
Any ideas??

 

OK, I'll pitch in! You can forget P1111 - this is a dummy code simply to indicate that all the diagnostic tests have completed.

The fact that you are getting a P1647 reference to O2 sensors leads me to believe that you have a 99 AJ27 engine (confirmation would be nice).

If so, P1647 is likely not causing your lurching. The usual cause of this code is an open circuit sensor heater on the B-Bank pre-cat sensor (the A-bank pre-cat code is P1646). I had both gone on mine when I bought it and no such symptoms on yours. If you have any doubts try to swap the sensors over if the wires will reach and see the diagnostic code change.

By elimination P1642 is likely to be your culprit, however according to my list it indicates a CAN link circuit error and could be anything from a faulty module to a dirty connector. P1642 will put you in fail-safe mode.

To be sure more detail is needed to confirm engine type, the code list differs from engine to engine and you need to check the right one or you'll be off on a right royal wild goose chase.

Jim

 

Thanks Jim, Yes, it appears it is the AJ27 engine. Checking code definitions I knew I I would probably be on a wild goose chase unless I learned a bit more.

It has stopped going into failsafe though. I will try switching the sensors as you suggest first warmer day. Dang cold front hitting today.

Thanks and I will keep you updated.

 

Jima:
I contend (but cannot prove!) that many, if not most, code P1642 reports are an artifact of connecting the code scanner to the data bus. I base that on no reports here that found a root cause problem with the bus wiring or modules after a report of P1642, and my own experience of the CEL coming on AFTER a connection, with only code P1642 showing.
I agree with your other points though, so I have no explanation to offer Ken.

 

That sounds entirely plausible to me - it's a bus and all devices on the bus must co-operate peacefully or contention or blocking will occur. I have my scanner specifically NOT set to 'Auto Comms' but to ISO only so that it will not flood the CAN bus with communication attempts. The modules on the Jaguar CAN bus are designed to inter-operate so that lower priority modules can not block a high-priority device so that e.g. your heater doesn't hold up your ABS module comms! Ken, if you have such a setting on your scanner you might care to try it. If it removes P1642 it won't cure your lurching but it will be another one eliminated.

Jim

 

Ken, what you see is a "by-product" code. If yo have a misfire you'll definitely set off an O2 sensor code, and if you have a scanner I'll bet you'll see an O2 sensor rich code code. Any misfire is due to a cylinder not firing, this will cause unburned fuel as a cylinder is not firing. This could be caused by a bad ignition system (coil, or plugs not firing) or fuel system not delivering enough fuel causing limited fuel flow that could range from wiring to or the ignition/fuel parts themselves. As you're not getting a misfire code it seems the problem is your fuel system.
You could have a fuel pump that's going bad too and that's why you're getting a 1642 code which is fuel pump circuit high input. Remember, an O2 "sensor" is only what it is, a sensor. It is basically a fuel trimmer and does not control fuel pressure.

Alan.

 

Thanks for your ideas guys. I guess I have let the computer codes intimidate me. Until the late 80's I was the neighbor everyone brought there cars to for help, now I just stare blankly under the opened hood.

Now I just need to do what I would have done on any pre-computer car. I will begin pulling the plugs to see if it is just one cylinder, a bank or all and go from there. Alan, you may be right about the fuel pump as I did a no-no just before this happened and let the fuel tank run nearly empty. That is why I changed the fuel filter which was indeed clogged.

Would the air intake temperature sensor cause this much of a problem as that was one of the code definitions mentioned?

I will keep you updated on my progress and any other ideas are greatly appreciated.

 

Weather it's spark or fuel you could pull coil connections one by one to isolate a bad cylinder (if it's just one).
If the misfire is random at least this might help determine that.

 

Dear Ken,

Definitely the IAT can cause more misfire when cold as the engine requires to run richer when cold. Most of these sensors are "thermistors" which means they have less resistance when they heat up. Without taking it out you can use a high impedance multimeter and check the resistance when cold and hot. High resistance when cold that decrease with higher temperature. Otherwise just make sure you have variable resistance when cold and when hot.

Alan.

 

Ken:
Get a fuel pressure test guage (less than $50.00) with enough hose to place the guage under the wiper while connected to the fuel pressure test schraeder port. Then monitor the fuel pressure while driving. The fuel pressure should remain abot 40- 42 psi above manifold pressure (vacuum) or between 35- 42- psi on a NA model.

 

Ken, you seem to be getting some conflicting information so it's not surprising you are a little confused. There is no reason to mistrust OBD codes as long as you understand what they are and where they are coming from as there is a 'generic' set of Jaguar codes but each model varies slightly from this and often has some additional codes. Let me try to correct some of the misinformation. My source is the Jaguar JTIS Technical Information System based on a '99 AJ27 engine (post Vehicle Identification Number 853936).

Firstly, the P1111 code is a system readiness code only meaning "System checks complete since last memory clear".

Secondly, P1647 indicates a 'control malfunction' with the O2 sensor - note, NOT misfires or rich/lean mixture which have their own set of codes. If you are lucky this is a bad connection to the sensor, if less lucky it's a bad heater in the sensor, if you are really unlucky it's a bad EMU.

Note: you can put a multimeter on these babies all you want but you will only be able to determine the heater continuity (approx. 6 ohms). If you try to meter the sensor itself you risk toasting the sensor part completely with the current the meter supplies so DON'T do this. The upstream sensors are constant-voltage wideband linear sensors which do not have a variable voltage - you can safely confirm this with any oscilloscope monitoring the sensor output - it's around 4 volts +/- a bit of electrical engine noise.

P1642 is 'Can circuit failure' - if it was a faulty module you might expect some additional codes to indicate which one which lends credence to sparkenzap's strong feeling about some code readers triggering this themselves.

Which reader are you using?

Now, from the 'generic' code list P1111, P1647 and P1642 respectively are:

P1111 Intake Air Temperature (IAT) Sensor Circuit Intermittent High Voltage
P1642 Fuel Pump Monitor Circuit High Input
P1647 Linear O2 Sensor Control Chip (Bank 2)

It is also quite possible that the codes you see do represent a fault/faults but are not related to your problem. Before you go off chasing faults you don't have you should decide which codes and their meanings you will recognise. Choose wisely :-)

Jim

 

Ken:
Which code did you think was IAT? Not that your IAT might not be bad, BUT you've no code related to that. P1111 is sometimes incorrectly reported as IAT, but that code is definitely "Drive Cycle Test Passed"

 

I don't know if you know what a "high impedance" multimeter is but it definitely won't "toast" anything.

Alan.

 

Jima-
Talk about misleading- I'm sure you di dnot mean to add to the misinformation, but in your post you recite P1111 as both IAT (misinfomation in the case of an XJ8, which this is) and Test complete (which is coirrect).

 

I sure felt that too, Ross. If I wanted help I would be more confused now than when I first started.

Alan.

Alan.

 

I beleive he was suggesting that when using the meter as an Ohm meter (measuring 'continuity' in his description), the voltage across the test leads, and subsequent current sourced through the sensor, could damage the sensor - don't know whether this will happen or not, but that was my take on his statement. "High Impedence" refers to the Volt meter's shunt resistance. Ohm meters are typically current sources, and are therefore inherently low impedence.

 

My $.02 (probably worth less)
Actually everything in all of these "conflicting" posts is pretty much accurate, as far as I can tell - BUT misleading.
By Jima giving both the generic and the Jaguar meaning of code P1111 it became misleading and therefore misinformation (which was his word!). The code only means one thing on a X308 and that is "Drive cycle complete". It gets replaced with P1000 when you reset the obd system until the cycle completes again.

As to the multimeter, I suspect the issue is that only part of the story is explained by the words "high impedence". A multimeter with a mechanical movement is genrally "low impedence" and a good digital meter (like any of the flukes) is "high impedence".
If we are measuring voltage, like we might on a wide band lamda (o2) sensor , then a LOW impedence meter means that relatively large current will be diverted to the meter to be used to measure voltage. I do not know if it will "toast" any circuit on the XJ8, but it will give bad readings on some circuits, in that the meter will "draw down" the voltage. A high impedence meter uses less current, therefore disturbs the circuit leass.

If we are measuring resistance, then meters that are rated "high impedence" will use less current to measure the resistance, and are less likely to damage a sensitive sircuit.

Now, as to measuring the IAT, I guarantee that either meter type will accurately, and safely measure it. But we have no code for it in Ken's case.

Ken:
As to your problem at hand, as Jima implied, you actually need to do what you always did to diagnose a problem, its just that you have different tools and methods to do so with the computer controls. That is, consider the data to determine likely causes. (Google "Occum's razor") Then pick the most likely and test to determine if it is the root cause. If it is, fix it. If not, try the next one. Now, in your case, I don't believe either of your codes is a "smoking gun" to match your symptoms. I would suggest you reset the codes, then drive to see what returns. Back to you saying that you would pull plugs to find if it is one or many cylinders, in my experience, the "misfire detect" code on an XJ8 is pretty accurate IF one cylinder is misfiring. Therefore I would look at the probable cause I mentioned before, and that is the fuel system. In my experience, low fuel pressure can cause misfire, without codes, but with "restricted performance." Your results may vary. Good luck, and keep us posted.

 

Well, re-reading it I thought this was quite clear:

"Firstly, the P1111 code is a system readiness code only meaning "System checks complete since last memory clear".

Listing the generic set which has been misleading him (and perhaps others) and suggesting Ken decides which to follow did not (and does not) seem misleading to me. I'll let Ken be the judge of that.

Jim

 

Yes I do, and when measuring resistance they still apply a small voltage to what they are measuring such that a current will flow and from Ohm's law the resistance can be calculated as R=V/I. Typically this small voltage will vary according to the resistance range selected, usually being highest when measuring diodes in order that it can overcome the forward current threshold (typically 0.7 volts) so that it doesn't look open circuit in both directions.

In the context of O2 sensors (which is what I was quoting) I have seen several knowledgeable specialist sources warn against trying to measure the sensor part as there is a risk of damage. I am happy to take them at their word and I certainly wouldn't want Ken trying this on his O2 sensors assuming they were like thermistors (which are basically just temperature sensitive resistors) and risking losing the other one.

Jim