Is there any other reason for code 1 to show up after running for 5 or so minutes?
Crank sensor showed 1450 ohms
Changed it for the spare 1450 ohms and still after 5 minutes running check engine1 shows up, drop in RPM, ruff idle, if I turn it off for 10 seconds and restart, check engine shows up again after 5 minutes.

Three different 02 sensors and two different crank sensors, I must be missing something.

Please help 1989 xj40 3.6

 

I still have the check engine code 1 coming up after 5 minutes running.
I have changed the crank sensor for a spare and the same thing happened.
Ohms are 1500 and when submerged in hot water they climb to over 1600 ohms.

Any ideas are most welcome

 

Hi muzz,

I've seen your posts in three different threads and the XJS forum and have moved two of your posts here to start your own thread. We frown on multiple posts in different threads and forums related to the same issue, since this can lead to replies from multiple members who may be unaware of information supplied by other members in other threads. It is far better to have all the discussions related to the issue together in the same thread.

I am not aware of any code that is flagged for CPS malfunctions on any of the XJ40s. On a 1989 XJ40, code 1 indicates a problem with the oxygen sensor electrical circuit being open (not a complete circuit, due to a disconnected connector, broken wire, corrosion on the sensor threads/exhaust downpipe, or a failed sensor).

I know you saw this chart I posted in another thread. This is from the Haynes XJ40 Repair Manual:




You can download a U.K. edition of the Haynes manual (missing chapters 7 & 8 but otherwise complete) from this forum at the link below:

Haynes Jaguar XJ6 XJ40 Repair Manual

Another helpful document that applies directly to the 4.0L engines but is also generally relevant for the 2.9L, 3.2L and 3.6L engines is here:

AJ6 4.0L Engine Mangagement System / OBDI Diagnostic Guide

Regarding the oxygen sensor (O2S or HO2S for Heated Oxygen Sensor), at startup the engine control module (ECM) ignores the signal from the O2S to allow it time to heat up to operating temperature, which is at and above 300C/572F. This period of operation is called "open loop," meaning the ECM determines the air-fuel ratio based on tables programmed into its memory with no input from the O2S. When time allotted for the O2S to warm up is complete, the ECM then begins referencing the O2S signal to dynamically adjust the air-fuel ratio. This is called "closed loop" operation or fueling. If the ECM does not receive a plausible signal from the O2S within a given time, a diagnostic trouble code (DTC) will be flagged (I believe this also illuminates the Check Engine Light).

This is why O2S problems may not show up immediately at start-up, but a few minutes later, when the ECM begins to expect plausible signals from the O2S.

Cheers,

Don

 

Thanks for fixing my tread Don B,
It seems highly unlikely that all three o2 sensors would have the same affect to trigger check engine, should I clean up the threads and contact area?

 

Hi muzz,

Do you mean that you have tried three O2 sensors and the check engine light continues to come on? If so, have you checked the rest of the O2 sensor electrical circuit, beginning with the 12V heater power supply that arrives from the fuel pump relay on the Blue/Red wire at the harness electrical connector for the O2S? Also check for continuity to ground on the black wire. Check for some resistance (more than 0 ohms but less than infinity) across the pins of the O2S electrical connector that correspond with the Blue/Red and Black wires.

Corrosion on the ECM electrical connector pins is also a known issue, as is corrosion on the ground points referenced by the ECM, two on the intake manifold studs and one on the bulkhead/firewall behind the cylinder head.

It might help us help you if you could start at the beginning and tell us the exact symptoms you are dealing with, when and how they first appeared, and any other issues that may also be occurring.

Cheers,

Don

 

I found the ohms to be infinite so a short, after a little more inspection i found this.


It looks like it goes all the way to the ecu. Big job but I have started.

 

Infinite is 'open circuit', ZERO ohms would be a 'short'.

That harness is a mess.

bob

 

Can the o2 sensor have a fuse or relay that may cause this to over heat?

 

Hi muzz,

Please add the year, model and engine details of your Jag to your signature line so we don't have to scroll back to your first post to be reminded.

Overheating is typically caused by excessive current draw or proximity to hot components (such as exhaust pipes). If the wire was routed too close to the exhaust downpipe or manifold, that could have caused the deterioration. Or, if its insulation deteriorated and the wires touched, or the sensor failed internally creating a short-circuit, this would have drawn excessive current through the wires and melted the insulation. There is no fuse in the O2S circuit directly; the O2S heater receives its power via the fuel pump relay, which receives its power directly from the battery via a splice in the battery positive power circuit.

Given the condition of those wires, it certainly seems possible that the fuel pump relay has been handling excessive current, which could damage its internal contacts. It might be prudent to replace the relay just in case.

Cheers,

Don

 

Thanks Don b, When I bought the car, the fuel pump was very noisy and running on 4 cylinders.
After finding a rusty fuel tank, blocked filter, blocked injectors, rusty fuel rail, broken regulator, leaking injector o'rings, rear suspension collapsed, cluster not working, powa-rac, leaking from boots, oil cooler leaking, door handle broken, central locks actuators broken, IR locking with no fob, Gear change bang, Steering pump leaking, A/C vents broken due to vacuum chamber behind the vent, ICV broken, Temp sensor faulty, Front upper and lower bushes flogged out, Ball joints warn out, steering pinion leaking,


Can I add to the list later, all this I have repaired on my own so this little problem is easy.

 

Hi Don B, I had some time today to trace the melted o2 sensor wires today, they trace back to the relay under the dash.
There is another larger blue with red stripe wire along side of it that looks to be melted. I think the wire has been stressed some how.

 

Hi muzz,

I have moved your post here from cooldood's thread, so all the information related to your car's issue will be together here in this thread.

The Electrical Guide will help you identify that Blue/Red wire - you can download the manual here:

Jaguar XJ40 Electrical Guide 1988-89

Cheers,

Don