Car: 2001 XKR Convertible made in July 2000. Approx 75,000 miles
First I want to acknowledge the incredible help that I have received from this forum and its members. All the following internet URLs are the wonderful result of those people who have made it possible for me to fix my car and I want to thank them for their assistance.
This info worked on my car. It may not work on your car. Use at your own risk.

Tuesday 8-11-15 was very, very hot day. Drove car to SA & stopped at NB about noon (Harbor Freight, Chinese Buffet – lunch). Went to Costco then to Sam’s and another store at 5PM. Car sat in sun all day and was extremely hot inside. Left store about 8PM and drove a mile. Car went into FAIL SAFE mode with TRAC NOT AVAILABLE & ASC NOT AVAILABLE. Turned off car and restarted. Seemed OK then did it again 2 more times. Car seemed to miss slightly. Drove about 20 miles to grocery store at no more than 50 MPH. If punched gas it would go FAIL SAFE ETC and require restart. Was in grocery about an hour and came out and car started normally. Drove on about 15 miles. All ok but hadn’t punched gas yet. Punched gas. Car went FAIL SAFE LIMP MODE again. Shut off and restarted 2 or 3 times but could not get it out of LIMP HOME MODE. Limped to gas station and shut off for ½ hour. Restarted but was still in LIMP HOME MODE so drove it slowly home.
For the previous several months car would briefly show “RestrictedPerformance” light and then it would go out and the car ran normally until 8-11-15. Think it possible that the excessive heat had something to do with it perhaps causing cracks in vacuum lines or fittings or need new brake light switch due to heat expansion.

CODES ON 8-15-15
P0171 System Too Lean (Bank 1) limits engine speed to3000rpm
P0174 System Too Lean (Bank 2) limits engine speed to3000rpm
P1121 Throttle Position (TP) Sensor Circuit Intermittent High Voltage
Causes Limp Home mode
P1646 Linear O2 Sensor Control Chip (Bank 1{A}) UPSTREAM (most likely)
Or Fuel Pump Relay 2 – malfunction cause: wiring, fuel pump relay
P1111 Intake Air Temperature (IAT) Sensor Circuit Intermittent High Voltage
Or System checks complete since last memory clear (most likely)

Bought new battery Group 49 Autozone Duralast H8-AGM $175– 10% discount and installed it. No FAILSAFE MODE but car seemed to not run right. Was missing slightly and slow throttle response.

Checked fuel pumps. Removed relays for both pumps and used short wire to jump socket terminals opposite and perpendicular to each other for each relay. Both pumps ran. Then used short wire to actuate both relays against 12v battery terminals. Both relays clicked indicating probably ok.
https://www.jaguarforums.com/forum/xk8-xkr-x100-17/99-02-xkr-owner-you-running-just-one-fuel-pump-85882/

Upon inspection of ECM while it is still in car observed that the guaranty seal on the side of the ECM had been torn in half indicating someone had opened it up before I bought the car. Also the two 5 amp fuses in the extra fuse inventory are gone. The ECM uses 5 amp fuses. This indicates there has been trouble with the ECM before I bought it. There is also a 25 amp fuse missing from the fuse inventory. Also the Jaguar fuse removal tool is missing.

Obviously there have been problems with the ECM before I bought the car.

Replaced brake pedal switch (brake light switch).
http://jagrepair.com/XK8BrakeSwitchReplacement.htm
https://www.jaguarforums.com/forum/xk8-xkr-x100-17/o2-sensors-brake-switch-replacement-problems-148529/

Replaced all 4 O2 sensors on catalytic convertors.
https://www.jaguarforums.com/forum/xk8-xkr-x100-17/how-i-changed-o2-sensors-2001-xkr-150472/
https://www.jaguarforums.com/forum/xk8-xkr-x100-17/upper-lambda-o2-sensor-replacement-p1647-104872/
https://www.jaguarforums.com/forum/xk8-xkr-x100-17/oxygen-sensor-removal-cable-lead-resolved-79384/

Replaced NGK PFR5G11E spark plugs (color looked ok - 6chocolate brown and 2 medium gray ones - but center electrodes eroded down to sharp points) with NGK IFR5N10.
http://jagrepair.com/PlugReplacementXK8.htm
https://www.jaguarforums.com/forum/xj-xj8-xjr-x308-27/how-change-spark-plugs-03-xj8-72827/

Cleaned all wheel speed sensors.
https://www.jaguarforums.com/forum/xk8-xkr-x100-17/how-cleaning-wheel-speed-sensors-faq-37434/

I have a scan tool from ScanTool.net that I use with a 17" laptop. It allows me to create a "dashboard" as shown: oops - thumbnail is at the end of this post. I don't know how to place it here.

Checked for vacuum leaks: squirted throttle body cleaner around various places and listened for changes in engine idle RPM. No changes. And:

PART 1
HOW TO USE SHORT TERM FUEL TRIM TO CHECK IF HAVE A VACUUM LEAK – STARTS AT ABOUT 20:30 MINUTES/SECONDS. CHECK SHORT TERM TRIM AT IDLE. INCREASE ENGINE RPM TO ABOUT 2500/3000. IF SHORT TERM TRIM GOES DOWN AND THEN BACK UP WHEN RETURN TO IDLE – MOST LIKELY HAVE VACUUM LEAK BECAUSE AT HIGHER RPM THE LEAK HAS LESS INFLUENCE BECAUSE MORE AIR IS COMING THROUGH THE REGULAR WAY THAN PROPORTIONALLY THROUGH THE LEAK.

TO CHECK FOR A DIRTY MAF (MASS AIR FLOW) SENSOR – AS RPM GOES UP SO DOES THE SHORT TERM TRIM.
Cleaned MAF sensor (I thought.)

Replaced engine oil and filter.

Slightly adjusted accelerator pedal adjustment at throttle body.
THROTTLE CABLE ADJUSTMENT
Hlgeorge 7-04-2010 #41


Checked throttle for dead spots by pushing slowly and observing curve on scantool. All OK and have 100%.
PART 1
LOOK FOR DEAD SPOTS IN TPS – OPEN SLOWLY AND WATCH SCAN TOOL VOLTAGE (throttle opening %) FOR CONTINOUS RISE AND FALL AS SLOWLY CLOSING.

Did the “push accelerator down slowly” thing to adjust pedal position with ECM.

This eliminated P1121 throttle position code and P1646 O2 bank 1 upstream code.

Car now had P0171 and P0174 lean codes and with increasing throttle or full throttle short term trim was at 25 for both banks indicating not enough fuel. (Checked my 2000 Suburban which had 0.0 short term trim at full throttle.)

I went briefly berzerk!

Found thread (can’t find it again) which showed that I had NOT cleaned the MAF sensor correctly. I had only cleaned the wires on the side of the sensor. I didn’t know there were wires up inside that tube. Spray cleaned the sh&% out of those wires inside the sensor tube with CRC MAF cleaner. Now scantool showed 0.0 short term trim at full throttle.

Retracted berzerkness.

Car runs great (knock wood). On 10-10-15 only code showing is P1111 indicating completion of the diagnostic process. So far so good.
Hope this helps someone. Everything I did I learned from this forum. Thank you all.

 

Thanks Poet. That was a great piece. In your studies, did you run across any threads where the only CEL was P0171 "or" P0174 (not both) and the CRC MAF cleaner did the job? I'm just getting 0171 and a brief RP. I'd love to NOT have to take the supercharger off!

 

Hello scardini1,
No I didn't see anything like what you describe but I'd start by checking out any sensor relating to only the P0171 bank. Try looking for a vacuum leak somewhere in that bank and check the resistance in the O2 sensors for that bank to see if they are OK.
Good luck.