Hi Guys,
I have a CEL coming on with the codes P0172 and P0175 (rich on both banks) in my XJ8 2006 w/ 67k on it. First time it occured the CEL was accidentally reset by NAPA and it took almost 300miles to come on again. I do not feel any driability issues. The Indy that is working on this has checked for vacuum leaks and found a couple (MAF was ok) and send me on my way. It lasted 82miles before the CEL lit up - Indy still believe it is a vacuum leak. Does any of you have experience with this and would be so helpful to give some ideas?
Thanks
Martin

 

Hi Martin,

I am attaching pages 1312-1313 from the Powertrain section of the Workshop Manual, which you can download in six sections from this forum:

http://www.mediafire.com/download/md...f+contents.pdf
http://www.mediafire.com/download/aa...nformation.pdf
http://www.mediafire.com/download/n3...2.+Chassis.pdf
http://www.mediafire.com/download/9b...Powertrain.pdf
http://www.mediafire.com/download/0i...Electrical.pdf
http://www.mediafire.com/download/4j...+and+Paint.pdf


The P Diagnostic Trouble Codes (DTCs) are listed in the Powertrain section, and as you will see in the attached pages relevant to P0172 and P0175, there are numerous potential causes of those codes, none of which is a vacuum leak, which in my experience is more likely to cause running that is lean rather than rich.

When I read your account and the fact that both cylinder banks are involved, my first suspicion was the ECT sensor, or Engine Coolant Temperature sensor. The ECT provides an engine temperature signal to the Engine Control Module (ECM), which enriches the air-fuel mixture when the engine is cold. If the ECT is lazy it may be slow to tell the ECM the engine has achieved operating temperature, resulting in an over-rich condition. I believe the ECT output can be read with JLR SDD or possibly with any good OBD II scanner with Live Data capacity, but rough tests can conducted manually with an ohmmeter, since its resistance varies with temperature.

The ECT was my first instinct, but as you can see in the attached document, there are a lot of other possibilities, so you'll have consider the ones that are most likely. Since both banks are involved, I'd suspect a sensor first.

Hopefully someone who has had the same symptoms will chime in with a resolution.

Cheers,

Don

 

Don,
Thank you for the tables and the reply. ECT makes a lot of sense as this code first comes after a while when the car has reach operating temps. It will also explain why I do not really have any drivability issues, Indy just said he checked this and it measures the temp perfectly though he has not checked it through the operation from cold to hot. It also makes sense that any leak in intake after the MAF would result in a lean conditon, but what about a leak in the real vacuum hoses can that cause a rich condition ??
Martin

 

Hi Martin,

I haven't studied all the X350 vacuum hoses, but typically the source of vacuum for most vacuum hoses is the intake manifold, so when a vacuum hose develops a leak, it allows the engine to inhale air that is unmetered by the MAFS, so the ECM cannot correct for it by enriching the fueling. When you have more air in the Air-Fuel Ratio (AFR), by definition that is a leaner mix. I can't see how adding air could cause a richer mix, but that doesn't mean there isn't some mechanism or system in which that could happen. Note that none of the potential causes listed by Jaguar for your codes is a vacuum leak or intake air leak....

Cheers,

Don

 

Don,
Thank you again for your input. After googling I found one place stating that the P0172 and P0175 means that the fuel trim is turned up all the way but the O2 sensor still want more fuel - I dont know if that is a correct interpretation. So the code really means that the engine is running lean. I hope there are a tech that can chime in here and clear up this matter.
Thanks
Martin

 

Hi Martin,

I can't speak to the information you found by googling and whether it is accurate for any car, let alone a Jaguar X350. The most accurate reference for diagnosing and repairing issues with our cars is the Jaguar X350 Workshop Manual, and I uploaded the two pages used by Jaguar mechanics for diagnosing P0172 and P0175 codes. Did you read the possible causes and solutions? If so, why are you convinced that you have a lean problem? Does your car have other symptoms or codes you haven't mentioned?

Cheers,

Don

 

Don,
I am not convinced of anything. I did read all possible causes of the 2 codes and they all make sense. I asked the indy shop based on the information you attached about all the sensors and they are telling me they have checked all of them and nothing is suspicious. Like you pointed out a vacuum leak should result in a lean condition. The P0172/175 is bank 1/2 is rich and it simply did not make any sense that the shop was checking for leaks and I wanted to understand why. As I stated I dont know if the information about the codes meaning is correct but if the code actually is a lean condition code then it make sense the shop is checking for vacuum leaks - I hope I make sense? You have provided some very useful information to get to the bottom of this - thanks
Martin

 

The leak can also be in the exhaust

Check the 4 bolts on the exhaust flange where the pipes connect to the manafold.

See my post here LTFT Fixed

A smoke tester will also get the job done locating any leaks on the inlet side. I posted how to make one for a few dollars

See my post here https://www.jaguarforums.com/forum/x...17/#post976397

Cheers
34by151

 

Thanks 34by151
Yes it can indeed be a leak in the exhaust - I will let the shop know.

 

So after a long time, back and forth to the shop it was finally fixed. Shop was unable to detect any sensors as erronous but was able to detect some good vacuum leaks. These were repaired from the bigest to the smallest and everytime all looked great but after 100-200miles the car would set a code. Mass air sensor was replaced and there has been no code for 300miles and all monitors are perfect:-) The car is idling so much more better now - better than I remember it ever has done. The car has always had a less than a smooth cold start - I am pretty happy - thank you for your inputs!

 

Congrats!

 

I was throwing codes for the opposite, Left and Right bank Lean. Checked all over for vacuum leaks which seemed obvious. Even broke a brittle plastic vacuum hose to the PCV valve and replaced it with rubber. Still the codes came back.
simmular
Drove over to AutoZone and purchased a replacement MAF Sensor. Two screws and a plug to install in a minute. It fixed everything and the car ran better than it ever had. The throttle is so responsive it's feel like its supercharged. It would appear that the MAF Sensor degrades without throwing a MAF Sensor code causing other systems to compensate for bad info causing codes in my case and apparently this one. For $79.00 you may be surprised at the improvement in performance of your car.
Cardone Reman/Mass Air Flow Sensor (74-50009) | 2006 Jaguar XJ8 8 Cylinders 4.2L SFI DOHC | AutoZone.com

Give it a try Best performance improvement I have ever seen.

 

I am glad to hear that changing the MAF sensor helps with the P0172/P0175. Maybe I should try one of the auto zone MAF sensor instead of the Denso replacement which was made in Japan. Its very annoying to have the CIL on. Also thanks guys for keeping me posed.

 

From my research on X308, P0172 and P0175 can indeed be caused air leaks. The O2 sensors detect lean mixture and instruct the ECU to add more gas, this will happen repeatedly until both banks are running too rich then you will get P0172 and P0175, check engine light and possibly 'restricted performance'.

 

I really doubt that is true and strongly suggest anyone reading this adopts similar doubts.

 

Dead thread, but for clarity...P172/P175 means the trim is turned all the way lean, and the mixture is still too RICH. If the mixture were lean, it would trigger P171/P174. So...the codes the OP had are for RICH, and only RICH!

1) The only vacuum leak that could possibly cause this condition is the vacuum line to the ECM. Any other vacuum leak would trigger a lean code. When the OP found vacuum leaks, they were gravy, but did not cause the rich codes, as he verifies.

2) MAF will always be the primary suspect for a dual bank rich condition.

3) Secondary suspects will be the temp sensors (air and coolant), leaking injectors, and fuel pressure regulator.

 

It can also be caused by a leak in the exhaust up stream of the o2 sensors

Cheers
34by151

 

That will, once again, trigger a lean code. The O2 sensors would read lean and continue to richen the mixture until it hit the rich trim limit, and thereby set P171/174.

Everone is getting confused about the trim. If the trim hits the rich limit, you get a lean code. If it hits the lean limit, you get a rich code.

 

Yes that is logical, but a comment on the X308 forum from someone who had some work done at a shop said that the shop had broken off a plastic piece of the inlet hose between the MAFS and the TB. They had bodged it up with tape but the tape gave way when the motor was hot leaving a gap which would suck air, and he got P0172/P0175, which went away after he had repaired the hose. ?????

 

Sounds like an unreliable posts, with confused info.