I am a new user of this site so I apologize if I didn't follow any protocols. Here is my issue... I have been noticing my xj8 2004 go into the limp home mode for random reasons while I'm driving. When I look at the obd reader (autoenginuity's jaguar enhanced software) I get P0121 with P1582 (throttle monitor data). In the past when I got this I have cleaned the electrical connectors to the mass air flow sensor and the throttle position sensor. It seemed to have fixed it for a few months but now it is back again.
For some additional recent history, I got this error when I accelerated quite rapidly on to a ramp. The car went to the limp home mode not while I was accelerating but a few miles later when I slowed down after the exit. I imagine this had something to do with the fact that I floored it recently. After reading the codes I decided to reset the code and just try driving again. After maybe 10 miles of driving today I get the error again but this time for no special reason. I am planning to do the cleaning of electrical connectors again tomorrow since that seemed to have helped last time I went through this.
I would like the jaguar experts here to tell me what are the likely causes of such intermittent and somewhat unpredictable failures?

 

The cause is an incompatibility between the materials used to make the connections to the throttle body. The real fix is to replace the connectors and seal the connector plug so water does not enter the connection area. I will provide the TSB. I say this because I have been there done that several times, bite the bullet and replace the connectors.

Link to TSB http://jagrepair.com/images/TSB/XK8/303-58.pdf

Link to Topic P0121 JagRepair.com - Jaguar Repair Information Resource

I should mention that the TSB is for 1999 – 2001 and not 2004 but I would assume it is the same issue

 

If that doesn't 'fix' it, it most certainly is the throttle position sensor, if you read in the xk8-xkr area, they're very close to finding a source to just the sensor, as opposed to the current acceptable 'repair', which is a new throttle body. I've heard of more than one owner ending up going that route, and the hit to the checking account it incurs.

 

I been dealing with this problem for over a year. So far, i have replaced the pins for the throttle control, the two wires. That dramatically fixed the problem, but i still get the limp home from time to time. Next, i well be repaving all the pins.

 

Thanks Gus for the bulletin. I will check out the connectors tomorrow to see what type of terminals they are (gold or tin etc). Hope I can get the LNG3956AA part at the dealer.
Thanks H20boy for the suggestions as well. I will check those out.

 

Matt is correct in that it could be the throttle body position sensor and in most cases it will throw a P1121 code and if that is the case then a TB replacement or rebuild would be the next step.

Link JagRepair.com - Jaguar Repair Information Resource

 

Just an update on this issue. I got a chance to look at the connectors to the TP sensor and it looks like they are of gold tip kind and seemed more or less clean. I did notice that they are a bit lose when seated. I am wondering if I should still go ahead and replace the pins? Also is it possible to get the female connector part as well? Seems like that might still be an issue when I place fresh pins in because it doesn't seem to seat tightly.

 

Gotta watch the model years, fellas........

The TPS terminal bulletin applies to the x308 and not the x350. The x350 already has gold terminals. The P1582 only tells you flight data has been recorded, it's not really a fault.
Matt is right that it is most likely the TPS itself, which normally requires a throttle body. I'll be anxious to see if someone does actually find a source for those sensors; I'd sure be game to tackle a local repair of a throttle body.
Until it's repaired, the OP will probably have the limp mode occur more and more frequently.

Cheers,

 

Was this ever resolved?

 

P0121 is for the pedal position sensor. Replace the gas pedal assembly. It is multitrac and when the readings do not agree you get this code and limp home

 

Maybe, but I suspect it's likely to be the Throttle Position Sensor (TPS)

 

• G258127T11 - G258127T13

: DTC P0121; THROTTLE POSITION (TP) SENSOR RANGE/PERFORMANCE, HIGH/LOW VOLTAGE

G258127t11 : CHECK THE TP SENSOR SENSING CIRCUIT TP1 FOR HIGH RESISTANCE

1. Disconnect the battery negative terminal.
2. Disconnect the ECM electrical connector, PI01.
3. Disconnect the TP sensor electrical connector, PI26.
4. Measure the resistance between PI01, pin 75 (R) and PI26, pin 03 (R).

-Is the resistance greater than 5 ohms?

-> Yes
REPAIR the high resistance circuit. CLEAR the DTC. TEST the system for normal operation.

-> No

G258127t12 : CHECK THE TP SENSOR SENSING CIRCUIT TP1 FOR SHORT TO HIGH VOLTAGE

1. Reconnect the battery negative terminal.
2. Turn the ignition switch to the ON position.
3. Measure the voltage between PI26, pin 03 (R) and GROUND.

-Is the voltage greater than 5 volts?

-> Yes
REPAIR the short circuit to high voltage. CLEAR the DTC. TEST the system for normal operation.

-> No

G258127t13 : CHECK THE TP SENSOR SENSING CIRCUIT TP1 FOR SHORT TO GROUND

1. Turn the ignition switch to the OFF position.
2. Measure the resistance between PI26, pin 03 (R) and GROUND.

-Is the resistance less than 10,000 ohms?

-> Yes
REPAIR the short circuit to GROUND. CLEAR the DTC. TEST the system for normal operation.

-> No
INSTALL a new TP sensor. CLEAR the DTC. TEST the system for normal operation.

 

• G240070T8 - G240070T14

C : DTC P0121

G240070t8 : CHECK THE POWER SUPPLY TO THE THROTTLE POSITION SENSOR

1. Turn the ignition switch the to the RUN position.
2. Measure the voltage between the throttle position sensor electrical connector PI 26 pin 4 (OY) and ground.

-Is the voltage less than 4.5 volts?

-> Yes
Goto [G240070t9]

-> No
Goto [G240070t11]

G240070t9 : CHECK THE THROTTLE POSITION SENSOR POWER SUPPLY CIRCUIT FOR OPEN CIRCUIT

1. Turn the ignition switch to the OFF position.
2. Disconnect the ECM electrical connector PI 1 and the throttle position sensor electrical connector PI 26.
3. Measure the resistance between PI 1 pin 12 (OY) and PI 26 pin 4 (OY).

-Is the resistance less than 5 ohms?

-> Yes
Goto [G240070t10]

-> No
REPAIR the throttle position sensor power supply circuit from the ECM to the throttle position sensor. CLEAR the DTC. TEST the system for normal operation.

G240070t10 : CHECK THE THROTTLE POSITION SENSOR POWER SUPPLY CIRCUIT FOR A SHORT TO GROUND

1. Measure the resistance between PI 26-pin 4 (OY) and ground.

-Is the resistance greater than 10,000 ohms?

-> Yes
DIAGNOSE the electronic engine control system.

-> No
REPAIR the throttle position sensor power supply circuit from the ECM to the throttle position sensor. CLEAR the DTC. TEST the system for normal operation.

G240070t11 : CHECK THE THROTTLE POSITION SENSOR GROUND CIRCUIT

1. Turn the ignition switch to the OFF position.
2. Disconnect the throttle position sensor electrical connector PI 26.
3. Measure the resistance between PI 26 pin 1 (BG) and ground.

-Is the resistance less than 5 ohms?

-> Yes
Goto [G240070t13]

-> No
Goto [G240070t12]

G240070t12 : CHECK THE THROTTLE POSITION SENSOR GROUND WIRE FOR OPEN CIRCUIT

1. Disconnect the ECM electrical connector PI I and the throttle position sensor electrical connector PI 26.
2. Measure the resistance between PI 26 pin 1 (BG) and PI 1 pin 19 (BG).

-Is the resistance less than 5 ohms?

-> Yes
Goto [G240070t13]

-> No
REPAIR the throttle position sensor ground circuit from the ECM to the throttle position sensor. CLEAR the DTC. TEST the system for normal operation.

G240070t13 : CHECK THE THROTTLE POSITION SENSOR

1. Measure the resistance between PI 26 pin 2 and PI 26 pin 4.
2. Measure the resistance between PI 26 pin 3 and PI 26 pin 4.

•  
  • Are the resistor values the same?

-> Yes
Goto [G240070t14]

-> No
INSTALL a new throttle body.

G240070t14 : CHECK CONTINUITY OF THE THROTTLE POSITION SENSOR OUTPUT CIRCUIT

1. Measure the resistance between PI 1 pin 75 (R) and PI 26 pin 3 (R).
2. Measure the resistance between PI 1 pin 76 (Y) and PI 26 pin 2 (Y).

-Is the resistance less than 5 ohms?

-> Yes
Goto [G240070t15]

-> No
REPAIR the circuit from the ECM to the throttle position sensor. CLEAR the DTC. TEST the system for normal operation.

G240070t15 : CHECK THE THROTTLE POSITION SENSOR OUTPUT CIRCUIT FOR A SHORT TO GROUND

1. Measure the resistance between PI 26 pin 3 (R) and ground.
2. Measure the resistance between PI 26 pin 2 (Y) and ground.

-Is the resistance greater than 10,000 ohms?

-> Yes
DIAGNOSE the electronic engine control system

-> No
REPAIR the circuit from the ECM to the throttle position sensor. CLEAR the DTC. TEST the system for normal operation.

 

Pay attention to vin info. Totally different diagnosis. Also over the years i can tell you i have repaired more of these codes with a pedal assembly than a throttle body. This is one of the misleading codes that doesnt seem to be fully vetted between uk english and american english. Just offering up more to think about and check