Hi all,

I got a '98 Jaguar 3.2 X308/XJ8 Sovereign here that intermittently goes into limp home mode. At least i believe that's the english term; or emergency run mode freely translated from Dutch.

The weird thing is, there's nothing that is affected by it; during limp mode it revs freely to the maximum rpm, there seems to be no limit in speed or power either.
The garage says their OBD diagnostics can't talk with Jaguar ECU's so I tried it myself. They said the Jaguar dealer can diagnose the error, but there's no dealer near me.

I used my el-cheapo ELM327 adapter to find a fault code, but it says that there's no fault code stored in the ECU during limp mode. But I can real-time follow the engine's sensor's with the Torque app, and I saw something. Both downstream oxygen sensors of bank 0 and 1 did not seem to give any signal, while both upstream sensors reported the usual sinusoidal wave between 0 and 1V.
Furhtermore, a fully depressed accelerator only gives a TPS signal of about 80%.
The long and short term fuel trims are within reasonable limits, but the exhaust smells like it runs way too rich.

All signals that those downstream oxygen sensors are failing right? Or could it be something else like an air leak?
Is there a method to confirm a broken oxygen sensor?
Thanks for the help!

 

A quick and dirty test is to remove them ( don't mix up the connectors positions relative to the exhaust line holes ) and heat with a torch to remove the surrounding O2 in the video . This only shows that they function or move but not that they are calibrated or in range . Might need to change (or put in ) the PID's on the display configuration with the ELM327 on the rear sensors . Fuel trims should read 0.0 . On the TPS the most important point is the idle at 0 % and as you slowly motion through the throttle range you don't get a spike ( or open with a common meter ) in the reading . You can see this with a common meter or the ELM327 time line graph line

 

The TPS signal at idle is about 4% but the idle rpm is around 650rpm as it should. It's a shame you can't see the AFR the ECU is assuming, that would clear up a lot. Is it known why this engine uses 4 oxygen sensors though?
What is the point of 2 sensors if you don't use them to check the cat?
I'll try to test the sensors as you described, thanks for the help.

 

You should be able to pull up and see the AFR as one of the PID's in the ELM327 software

The second set of O2 sensors measure a change in cat through gas O2 as it is directly related to the other unwanted emission gasses . As a Cat (or sensors ) fails you will get a code 420 and 430 efficiency . You only need one set of sensors bank 1 and 2 to regulate the engine fuel trim . Soak the sensors in a shallow jar of gasoline overnight getting it into the cap vents to clean off crud and refresh them . Don't soak the wires

 

If you are anywhere near the Hague I would be happy to plug in my OBD scanner into your car. It can read all Jaguar specific codes.

Jeroen

 

Generally the rear sensors are used to fine trim the fuel trims. Also to detect failing cats.

 

tr7,

A common cause of restricted performance is a problem with the ABS system, such as a failing wheel speed sensor, dirty sensor, intermittent break in the wiring harness of one of the sensors, or poor solder joints in the ABS module. All of these problems trigger diagnostic trouble codes (DTCs) that begin with the C prefix (for Chassis), and cannot be read by most generic OBDII scan tools. To read them requires a Jaguar dealer-level diagnostic system or a higher-end third-party system such as Autoenginuity with the Jaguar enhancement.

Some of the other problems that can cause restricted performance or limp home mode trigger U (Network) codes, which are also not read by most generic scanners.

Rich running can be caused by an engine coolant temperature sensor (ECTS) that has failed at a "cold" resistance, prompting the ECM to continue applying cold-start fuel enrichment even after the engine is warm. This may not trigger a DTC if the ECM is receiving a plausible signal from the ECTS, even if the signal is incorrect.

Since you don't have any standard P (Powertrain) codes flagged, it would be worth finding a local independent shop with the system necessary to read the proprietary Jaguar C, U and B (Body) codes.

Cheers,

Don

 

I have looked into it and i think i'll be able to set up a PID to get the AFR. It shouldn't be too hard, and if so i'll ask here again.. Would be nice to see some AFR value. Regarding the sensors, i'll treat them with your suggested gasoline bathing and rinsing session and see if that helps. It wouldn't surprise me if they're full of sooth, since the owner(my grandpa) doesn't push the engine ever. But I really did the past few days hehe, and i have the feeling that it's getting better. But that could just be a placebo.. Are these sensors electrically heated, or only by the exhaust gas? Cause that could explain a soothed sensor.

 

Thank you very much for the offer! I live near Sliedrecht, but I work and go to school in Berkel and Rotterdam, so i get in the vicinity of the Hague often. The CEL hasn't come on anymore for the past 150kms but if it does, i'll be sure to make use of the offer. Thanks again.

 

I see. I've used the Jag the past week and pushed it pretty hard to check on it, but the ABS and brakes in general work very well. The ASC does its work perfectly also. There can still be a problem with those though. Is it possible for the ECU to have stored errors and restrict performance without the CEL lighting up? Because there is no detectable difference when it's either or not in limp mode. The CEL doesn't even light up at all. If so, I can check up with Jeroen who offered to help me with diagnosing errors.

Regarding the ECTS, the dashboard gauge shows a temp perfectly in the middle of the gauge after warming up. If that's coming from the same sensor, then the ECU should get out of the cold mode fine i guess. Thanks for the help!

 

Problems such as an intermittent break in the wiring harness of an ABS wheel speed sensor may trigger Restricted Performance without affecting normal brake peformance (the brakes will work normally with ABS completely disabled). Typically, you will get the ABS/DSC/ASC warning lamp along with the RP warning, though. But I wanted to give you an example of a system that can trigger RP without flagging generic OBDII Powertrain (P) DTCs.

Regarding coolant temperature, we have learned that the temperature gauge in the instrument cluster cannot be used as a guide to actual coolant temp. When the thermostat in our '03 XJ8 stuck closed, I used a scan tool to watch the temperature rise to 239.6 degrees Fahrenheit before the gauge needle began to rise from the center position!

ABS and engine coolant temperature are two of many systems that communicate via the CAN bus and can trigger problems that do not set Powertrain DTCs, so we'll look forward to the results of having your car scanned by a system capable of reading all the proprietary Jaguar codes and live data.

Cheers,

Don

 

The 98 X308 3.2 L engine only shows 2 sensors total . The heated portion comes from fuse 14

 

What should the voltage values be on bank1 and bank2?

My bank2 o2 sensor is reading 0 volts.

I get a reading from bank1

 

What kind of sensors do the elec diagrams for your (2002) car show? (At some point the fronts changed to wideband which are not voltage-based.)

Usually the two banks are (and should be) similar but be sure you're not being misled by a tool.

If you're not getting codes you can usually just look at LTFTs. They're more use than voltage/current numbers.

 

I've just changed a bad 02 sensor on my 2002 3.2, which has upstream and downstream sensors on each cat. Sadly in my case is was the LH Upstream sensor that had gone, the most awkward to replace. But it solved the issue straight away, and the car is noticeably better now. The downstream sensors are easy to remove, so as others have said it may be worth just pulling them and cleaning them.

 

Thank you.
I was looking at the wrong codes.

When I programmed the correct sensors into my OBD, they all came up.
Both sensors are reading almost identical, with some expected fluctuations I’m sure.

All looks normal.

I guess I’ll save the 4 new O2 sensors I bought for a time when there is a real problem....

Thank you for pointing me in the right direction.

 

They fail eventually so those will be useful spares. Don't beat yourself up!

 

I've soaked the sensors in a jar of gasoline overnight, and drove the exhaust really hot to burn of any remaining sooth deposists, and it seems that the problem is solved.
Should the problem come up again, than it'll obviously be time to replace them. Thanks everyone for the help!