Greetings All - I am new to join the forum although I have frequently read posts over the past few years as a guest when needing help. Current ride is a 2002 XJ Sport with around 70,000 Miles on the clock. Have not had any issues for the last 18 months, but all good things come to an end so several weeks ago the check engine light came on during a 1 hour drive. I cleared the code with my code reader (Innova) to see if it was a one off thing but it came back again and another code as well. The codes are;

P0443....EVAP Emission Control System Purge Control Valve
Circuit

P0446....Evaporative Emission Control System Vent Control
Circuit

Looking at other posts on the forum, it would appear that there are a number of different possible causes - purge valve, canister close valve, leaking vapor hose, faulty oxygen sensor among others. It seems like a daunting task to track down the culprit and was hoping someone has some thoughts on a reasonable way to approach this. I don't have a smoke generator to check for leaks but if this becomes necessary I will beg or borrow one.

Any advice would be appreciated.
Steve

 

Things I'd do:
1. clear codes and see which comes back first
2. stare at Electrical Guide looking for clues / things in common / etc
3. use IDS/SDD and hope it helps (get a Mongoose JLR...)

 

Thanks for the tip. I will wait for the DTC to pop up again and as the car drives with no problem, there is no urgency. I have been contemplating getting a more capable scanner (the Innova is next to useless for most problems, but it will erase P codes at least) but am unclear as to which is the best route to take as many think Autoenginuity is the way to go. Will advise how things develop in due course.

 

Hi Steve,

Since the system has logged codes that indicate a problem with multiple electrical circuits, it would be worth cleaning the ground points associated either with the evap components specifically, or the Engine Control Module (ECM). Resistance at ground points due to corrosion or looseness is known to cause lots of hard-to-diagnose gremlins. The Electrical Guide has a chart showing where all the grounds are located throughout the car, and the component lists associated with the Engine Management System schematics will give the locations of the grounds used by the ECM and/or Evap components.

I think the ECM uses multiple grounds, some of which are on the bulkhead (the Engine Mangement System or EMS grounds), plus a Logic Ground or Signal Ground, which may be at the left side of the engine bay (it's a ground stud to which Black wires with Pink tracer lines attach). Let us know if you have difficulty finding the locations from the schematics and we'll try to help.

In our '93, a recurring code associated with the carbon canister purge valve has generally been resolved by cleaning two grounds used by the ECM, so if one or both of your codes reappear, it might be worth cleaning the grounds (in Jag saloons it's worth cleaning all the grounds every few years and coating them with dielectric grease to slow the formation of future corrosion). I hope this info is helpful. Below is a link to photos showing how I maintain the ground points on our '93 and '04. I've taken photos of our '04 also but haven't managed to get them uploaded yet:

Welcome to Jag-lovers - Members Photo Viewing Page

Cheers,

Don

 

Don - Based on the Electrical Schematic there are 23 Ground Points located throughout the body. Some are indicated to be for specific components (ABS Ground Stud, EMS Ground Stud, Keyfob Antenna Ground, Etc.) which do not seem likely to be at issue. Others like the LH/RH forward Ground Studs and the LH/RH Bulkhead Ground Studs are more likely contenders. This weekend I will see if I can get to them without too much trouble. If not there is a friendly Indy who I can probably get to help. Anyway thanks much for the info, its not something which would have occurred to me but it makes a lot of sense.
Steve
2002 XJ Sport 70K mi
Ex- 1990 XJ40 Sovereign 190K Mi

 

Hi Steve,

You're right that many of the ground points aren't likely relevant to your issues. But bear in mind that resistances are cumulative, so if the ground for a sensor has increased resistance due to even minor corrosion, and a related ECM ground also has increased resistance, the signal processed by the ECM may fall out of the acceptable range, triggering a DTC. That EMS ground stud (Engine Management System, of which the ECM is the brain) would definitely be one I would clean along with the others you identified. If I recall, on the X308 the purge valve and vent solenoid are grounded through the ECM, so all the grounds referenced by the ECM should be suspect.

One other thought - low battery voltage is also known to cause erroneous DTCs. While you're cleaning grounds, it would also be worth cleaning the battery power connections on the bulkead and fuse boxes since even if the battery is in great condition, resistance in those power connections can reduce the voltage that finally arrives at the ECM.

Please keep us informed!

Cheers,

Don