Mechanics

FAILSAFE MODE

2000 Jaguar XJ8

Engine Mechanical problem
2000 Jaguar XJ8 V8 Two Wheel Drive Automatic 114000 miles

I have been receiving intermitting P0121, P0175 and P0172 but mainly P0121 codes. When I am driving on the streets the car goes into failsafe mode every couple of blocks and doesn't ever go into failsafe mode on the highway. When I turn on the AC that problem goes away for a while but when it comes back I only get a P0121 code. In the winter the lower valence was torn out by high snow and I wonder could this be the cause. I have replaced the throttle body and I am due for a oil change and the car runs good until the failsafe mode jump in. Need to know what is next as far as repairs? And what is the actual issues that need to be addressed?
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Hi
The codes you are getting are

P0121 THROTTLE POSITION SENSOR
P0175 B BANK TOO RICH
P0172 A BANK TOO RICH

Maybe a problem when you fitted the new throttle body but worth checking condition of the air filter.

Hope this is a starting point, if you need more detail please ask

stypejack

Tiny
Stypejack
Jun 24, 2010.
I know what the codes mean and I have treated the condition the best that I know how, but those problems are still there. I have replaced the air filter and throttle and I mainly get P0121 codes and the car goes into failsafe mode. Does anyone want to buy a jaguar? Lol I wish there was a way to erase the failsafe mode out of the ECU. It's dangerous anyway.

Hi

Not sure how much info you have or your backround so please bear with me.

Ok so as you know P0121 is TPS to ECM fault

P0172/P0175 could be incorrect signal from

ECTS Engine Coolant Temp sensor

MAFS Mass Air Flow sensor

IATS Intake Air Temp sensor

TPS Throttle Position sensor.

As P0121 is the most common error perhaps TPS to ECM is the main fault, however you say the problem is at its worst when driving slowly and I asume the engine will be at its hotest. When you put the air con on the fans cool the engine more and the error goes away.

It may be worth checking the temperature readings on the ECTS, MAFS, IATS to eliminate a wrong temperature reading causing the engine to adjust the fuel/air mixture.

I asume you have a obd code reader, free software is available to obtain the readings required via a laptop.

If all temperatures seem ok then its down to wiring fault between TPS and ECM or faulty ECM/TPS

Again sorry if this is going over what you know and have done already. Good luck.

Regards
stypejack

Tiny
Stypejack
Jun 25, 2010.
First, I would like to say that I am sorry if I appeared to have came off to you as someone whom didn't appreciate your help and/or assistance. I thank you very much. Now back to my issues. I have found out that my P0121 code was merely comming from my car going into failsafe mode, go figure and oil in my air intake fouled my mass air flow sensor (which was cleaned). But my car still goes into failsafe mode and I am wondering could it be my anti-freeze and/or my motor oil needs to be changed. I still get the dreaded failsafe mode and P0121 code but my car is running much stronger and longer before getting the code, must be doing something right. Thanx again.

No probs just everyone not at same level.

Still thinking along temperature reading fault.

Had a Maf damaged just by being a bit rough removing air box. It started showing very high air temp and I lost 90 % performance.

Fitted a after market cheap make and got 75 % back but not until fitted genuine part was the car back to 100 %.

Are you able to get these temp readings checked?

Regards
stypejack

Tiny
Stypejack
Jun 26, 2010.
Hi
wpuld really like to know how your getting on an if the problem is solved
sclassjack

Tiny
Stypejack
Jul 7, 2010.
Dear stypejack
reading marcus_jones post is like reading my own car log, I own a 1998 XJ8 with a rebuilt 4.0 V8 done in early 2009 and the car was running like a champ until I took it to a mechanic other than Crown Jaguar and I have had the same trouble since then. Random codes, high temp gear box, gearbox default, low coolant, bad rear bulb, ASC, stability control failure, traction control failure ABS and check engine light just to name a few, jaguar always states that nothing is wrong when I take it in however a few days later bam limp home mode, runs hot, and random codes and now the radio will not turn on and "PHONE" displays 24/7, I have tried to disconnect the CD player as stated by another driver and no help, I did replace the full load breather hose because it was dry rotted and allowed oil to get into the air filter and performance dropped, I noticed that it drove much better and then bam yesterday again here we go, I find that over the past two years this almost nerever occurs in the winter and always after the rain comes or high humitity, I live in Florida and that is almost all summer, Jaguar refuses to admit anything and states that they cannot duplicate my troubles even after I left it there for two weeks. Any ideas, ECM?

Thank You,
Crystal

Tiny
KMKOTARSKI
Jun 1, 2012.
Dear Dave you were right the cable slipped out I slid it right back in no further issues, I am now suspecting the TPS needs to be replaced, I cleaned the Throd Bod, MAF, new filter, plugs and checked OS and the limp home is still coming on. I made the istake of putting a lower octaine cheaper gaoline in the Jag and the intake was god awful dirty and sticky, I found an owner of a jag at http://www.jeevesandthejaguar.com/2011/09/shes-fixed-tps-problem-resolved.html who replaced his TPS without buying the entire unit is this plausable, I cannot trust anyone to work on my Jaguar but me and I really do not want to spend the money to replace it all, It is not all bad just the sensor please advise your opinion is very important to me, thanks

Tiny
KMKOTARSKI
Jun 15, 2012.
UPDATE to PHONE message on radio display: I located the sensor and Phone plugs under the arm rest and disconneted tem since I am not utilizing the phone system and the trouble cleared upon unplug, just wanted to state this if someone else has the issues, years of dust, grease, spilled beverages has caused a stickey goop in the transmitter under the console and shorted out the system.

Tiny
KMKOTARSKI
Jun 15, 2012.