Does anyone know the location of the 2 upstream O2 sensors on a 95 Jaguar XJS, thanks for any help.

 

I'll see if I can snap a picture later today, but you should see it with the hood open looking from the passenger's side of the car, just below the exhaust manifold.

Follow the pipes leaving the engine on the passenger's side of the car until you find them. If you have to get under the car, you've gone too far and have found the downstream sensors.

Make sure you change one at a time, so you don't plug the wrong sensor into the right plug.

 

V12 or AJ16?

 

Does this help?

 

I found them, pretty easy to change out. Thanks for your help.

 

USAF, I could be wrong here but I believe that on a 1995 4.0 the downstream are the most important ones. When I had my ECU reprogramed the gentlemen who did it for me told me the rears looked maxed out ( not fluctuating ) . I recently replaced them and my 96 has never run better.

 

You have it reversed. The upstream sensors are the ones providing the ECU with the values it needs to adjust the fuel air mixture, the downstream ones are there as a check to make sure the cats are functioning. As long as the value at the downstream sensors is lower than the upstream, things continue operating as normal.

That's not to say that a dying downstream sensor can't throw things off either. The upstream ones are definitely the sensors doing the heavy lifting in that system.

 

To reset the base idle, which do I get reprogrammed..the ECU or the ECM..? Im not getting any codes on the downstream Oxygen sensors only the upstream sensors.

 

1. You're still getting codes?
2. The TPS reset is something that happens when you plug your car into the Jag-specific device/software. Don't worry about that. It's a simple Procedure that literally takes two clicks of a mouse to complete.

As a matter of fact, I believe that the software can only do four things: check for codes (including transmission and ABS codes that standard readers won't pull), reset TPS, reset base idle and reorient oxygen sensors. Not sure the software will give a mechanic any other options. (The cloned mongoose and software package I bought let's me do all but the base idle reset, which is probably the most valuable to me)

ECU- Engine Control Unit
ECM- Engine Control Module

In the case of the XJS, the ECM is within the ECU, therefore they are essentially one and the same. People on these boards use them interchangeably.

On these cars, i wouldn't rely on the lack of thrown codes as a positive indicator. Getting codes for upstream oxygen sensors, great, change the oxygen sensors. Not getting a code on the lower ones doesn't necessarily mean they're good. Just not bad enough to throw a code.

This car is notoriously stingy with its desire to throw trouble codes when components are going bad?

 

Best bet here is a scan tool that, rather than just reading codes, will give a live data stream so the various sensor activities can be monitored.

But even that gets tricky as these early Jag OBDII systems and standard scan tools don't always speak to each other in the same dialect....at least that's the conclusion I reached when getting some readings that just didn't make sense


That was certainly the case with my 1995 X300 with the AJ16.

Cheers
DD

 

99% of the cars on the road are this way, the AJ16 engined Jaguars are not. Downstream is the important ones, upstream ( closest to the engine) are the check. I have no idea how they make it work that way, but that that's the way it works.

 

I really can't understand how the O2 sensors effect the Idle.

 

I should be in closed loop at idle, so the O2 sensors are controlling the fuelling.

 

Where did you learn this?

 

I just reread the manual- you are correct! It seems that the downstream ones provide the values that are used by the ECU for closed loop fuel metering correction, whereas the upstream are used for catalyst monitoring!

I just learned something today!

 

USAF
Specifically, what codes were you getting that indicated a fault on you upstream O2 sensors?

Also, your idle needs to be reset by someone with a PDU or equivalent. It will be the best money you spent on the car. Instant gratification as you hear your idle settle down. Before you go you might want to consider changing out your post cat O2's as well. In the PDU setup there is a reorientation of the O2 sensors. I know that sounds flakey but its on the setup screen.

 

USAF,
Maybe Guy Mace at the Springfield Auto Museum can point you to the right person with a (ready for the different names of the same animal) PDU or a WSD or a IDS or an Auto Logic programmer with a Jaguar XJS service pack (that's what worked on mine) Go read through my thread on 1996 4.0 High Idle.

 

The code I was getting is: P0152 High Voltage Bank 2 Sensor 1 I changed both them and now not getting any DTC's.