I have been trying to manage two sets of conflicting codes P0171, P0172 P0174 and P0175, i.e fuel too lean/rich on Bank 1 & 2. The CEL stays on with "Restricted Performance" emerging and disappearing intermittently. Replacing the MAF sensor only bought me one day's relief. My mechanic and I thought of the fuel filter - but replacing it only gave me another day of relief. The CEL and "Restricted Performance" warning and those codes have since all come back.

The "Restricted Performance" usually emerges when engine is cold, during slow traffic, or after car has been parked for a while. The engine would otherwise runs fine, although it does hesitates periodically especially during cold start or acceleration during operational temperature. Highway cruising is normal.

As the conflicting codes involve both banks with intermittent recurrence despite MAF sensor and fuel filter change, how likely are the O2 sensors, engine coolant temperature sensor and fuel pressure regulator the prime suspects? My ELM 327 is not working too well with my iPhone so I don't have live data to dig deeper.

I have done research on these codes in this forum, but none of previous posts is able to shed light on common causes and solutions.

 

How many miles on the odometer?

 

Nearly 90,000 km.

 

Not far from the MAF sensor there is a 1/2 " plastic tube running to the Left bank PCV to the intake flex hose. More than likely there is a slight air leak from the quick connection O ring not seating 100% and clicking into place. Add a little white grease on the o ring and reinstall. It will be a very snug fit and push till you hear the click. If when you find the line you can remove the end from the intake side by not releasing the locking mechanism this is very good news for you.


Took me a week of research to find this...

 

Many thanks for the tip-off. I shall investigate and fix if indeed there is a leak as you suggested. I knew that vacuum leak could be a probable factor for the dash warning, but would imagine that the warning should stay on rather than coming and going, and the leak should only affect Bank 1 rather than Bank 1 and 2?

 

A vacuum leak is the most likely and may be intermittent.

Monitoring LTFT's will tell you more.

 

Hi Qvhk,

The fact that you have codes representing both lean and rich conditions is certainly unusual. Reviewing the list of possible causes of those codes, the one that is identical for both the lean and rich codes is: "ECM receiving incorrect signal from one or more of the following components: ECT sensor, MAF sensor, IAT sensor, IP sensor, EFT sensor, TP sensor."

One possible cause of the ECM receiving an incorrect signal is corrosion on the ECM electrical connector or water ingress into the ECM. It would be worth shining a light under the cabin air microfilter housing in the engine compartment to see if there are any signs that leaves, seeds or other debris may have plugged the drain and allowed water to pool around the ECM connector.

If you don't already have the DTC Summaries guide you can download it here:

Jaguar X350 DTC Summaries Guide

Cheers,

Don

 

Sounds reasonable; I just hope it is not the ECM itself. I already had a real bad experience in ECU corrosion due to water ingress in my XJR6. Wish Jaguar had stronger protection of neural parts from the elements.

 

My '99 XK8 (4.0 non-S/C) has almost exactly the same problem with the RP light coming on at stop lights, idle speeds, etc., but on the road going away. Only P0171 lean on bank 1 but can't pinpoint the real problem and don't want to just throw parts at it. Cleaned MAF, replaced suspect coil, checked everywhere for air leaks (have you checked the VVT air seals for leaks?) but so far nothing.

 

Today on a long trip to the airport and back the CEL and RP light suddenly both disappeared - the CEL used to stay on. However after I plugged in an ELM 327 to scan for codes the CEL light has returned. I actually saw a Christmas tree with all warning lights turned on, together with a red light for "Low Brake Fluid", and "Gearbox Failure".... Such error messages were inaccurate. I immediately detached the ELM scanner as itself might be causing all sorts of abnormal readings. I shall have to continue to track the root cause for the RP warning. There are just far to many possibilities - many sensors involved, apart from air leak somewhere in the system.

 

The pattern of the "Restricted Performance" (RP) message emerging is when car slows down after perfectly normal highway cruising, and warm start after parking for an hour or so. During cold start the RP message might not emerge, but I can feel the engine and exhaust running slightly low, somewhat deprived of air or fuel. When the RP message is hoisted, the engine would hesitate during acceleration. I suspect that these symptoms may be temperature-related. Maybe I have a defective temperature sensor (affecting both banks), or the O2 sensors are giving up.

 

If you're using the Torque Pro app with your ELM327, you can monitor the coolant temperature sensor, intake air temperature sensor, fuel temperature sensor and O2 sensors.

 

Make sure that the exhaust is not blowing at manifold or the cats

 

I don't have much luck with the ELM327. The Torque Apps does not work on my iPhone. When paired up with the EOBD Facile Apps, ELM327 detected the fuel lean/rich codes but did not provide live data (it said "not supported"), and when I used the paid DashCommand apps, the ELM327 suddenly went crazy with all dash warning lights coming on and all sorts of text warning coming out from the central dial. I immediately removed the ELM327 fearing that it might cause unknown damage to the ECU or harnesses through the OBD socket.

I need to find a reliable scanner to help me diagnose the real problem. Right now there are just far too many possibilities (air leak, dozen of sensors) - don't want to throw more parts in blindly and getting nowhere.

A very noticeable sign is engine trembles mildly on cold start (can feel and hear from the exhaust as well). Step on the gas to hold for a few seconds then the engine would stabilize as it should.

I imagine that a leak is a leak and would generate constant but not intermittent warnings. If there is an air leak the volume of extra air sucked into the system, such situation would be caught by the system and trigger more dash alerts. However, strangely the RP dash alerts habitually go away during highway cruising. The RP warning also does not emerge during cold start, although as described above the engine looses stability during cold start. There have been no other DTCs excepts "fuel too lean/rich".

 

Borrow an Android device? Or buy a dirt cheap one?

 

I suppose I could borrow an Android device, but now the ELM 327 seems to be playing up. I can make a visit to a proper workshop to check up, but Hong Kong is not where you want to upkeep a Jaguar. The dealer is ultra-expensive; there is only one independent Jaguar workshop but earlier visits have discouraged me from making further visits. It lacks the knowledge and language competency to use the diagnostic tool well. It is getting by because it is the only alternative to the dealer.

Is it really impossible to diagnose the problem with my car without relying on OBD scanners?

 

The over fueling fault was due to an exhaust problem. Basically the exhaust was not seated on the manifold correctly and was thus blowing/sucking in air (venturi effect). As I have a loud exhaust anyway it was difficult to know if there was a problem there. I changed everything, all Lambdas and MAF to no avail. The code was running lean bank 2 but in reality it was running rich and turning the exhaust tip on that side black. The extra air being drawn in and past the upstream Lambda was causing it to register a lean burn and the car was then adding more fuel.
thanks Jerry interesting
This guy had a similar problem in the uk

 

It is unlikely, but I shall check carefully to see if I have any exhaust issue.

 

All of the above sound like wild guesses. You can't diagnose modern cars without data to see when/where/why the PCM is flagging these codes. You'll end up throwing parts at the problem with no resolution.

A vacuum leak at the intake would not cause rich running codes.

Just to play devil's advocate--one scenario (off the top of my head) is that the fuel pressure is stuck at one set value. If this happened, idle would be too rich and off-idle would be too lean. These vehicles use a returnless system where the fuel pressure is regulated for all rpm/load conditions. The PCM may not be flagging a fuel pressure issue unless it's out of range of the sensor. Don't take this as my diagnosis of your particular problem--I'm just point out that "running rich" and "running lean" are 2 of symptoms, not the underlying issue.

As a start, view the freezeframe data for the codes and see what conditions set rich vs lean.

 

The short answer is..... it's a hell of a lot more difficult to trouble shoot when you don't really know what's actually wrong.

The systems are too complex and too interrelated to allow flying blind unless you just want to throw parts at it until, as if by magic, you hit the right combination. Even then you run the chance of spending a lot of $ and still having the same problem.

I've used a product labeled OBDlink SX that includes the updateable software and the OBD II cable and can be used on any laptop or Netbook that runs at least Windows 7 for the past 3-4 years on both my '99 XK8 and my 04 XJ8. Can be bought on eBay and they're currently listed between $30 and $40 depending on vendor.

I bought direct from Scantool.net here: https://www.scantool.net/obdlink-sx/