SYMPTOMS:
car 2004 x350 NA in limp home mode,
display reads: "engine system fault, dsc not available and park brake fault"
DIAGNOSTIC EFFORTS:
using a sears innova code reader got code P1251
checked and cleaned connectors to throttle position sensor and throttle motor
checked continuity from relay fuse/relay box connector EC19-5 to ECM pin 52 is GOOD (less than .1 ohm)
checked continuity from ECM pin 134 to fuse 24 is GOOD (less than .1 ohm)
assuming that voltage to throttle motor relay is good because voltage to ignition coils and fuel injectors is good (engine runs in limp mode)
What to do next ?
1. open fuse/relay box and identify solid state relay and replace it ?
2. replace fuse/relay box (part costs about $700)
3. replace throttle body (part costs about $600)
4. something else ????

 

There are a lot of threads on this issue. Usually the throttle body position sensor is the culprit and the whole throttle body needs to be replaced as the sensor is not sold separately.

There are a few links where you can get the replacement TB for an affordable price ($150-$200)

 

If you need a throttle body, order it from Just Jags UK. It is about 130 pounds or $250. I got one to keep as a spare at that price.

 

Chances are that it will be the TPS and it is now available seperately,search

this forum for details, I think it is about $100.

PM Cambo for details if you can't find it.

If you replace the TPS I suggest that you follow this procedure:

Photograph position of existing sensor showing position of both holding

screws in the slots.

Remove old sensor.

Fit new sensor in the same position.

Photograph new sensor in position and compare photos.

The "proper" way to do this is to set the sensor to a voltage but the above

should be sufficient.

I have not had to do this myself but anyone who has please chime in.

 

I would also say check battery to be honest.

 

Battery is fine at 12.46 volts. Starts the car and runs in limp mode.

After resetting the OBD code, I put my voltmeter on fuse 24 (output of the throttle motor relay) and had an assistant turn the key to position II.
No voltage !

Voltage on fuses 12 an 13 are fine (B+) which per my circuit diagram also feeds to the switched leg of the throttle motor relay.

Looks like the throttle motor relay is not working.

Why would you think that the Throttle body/Throttle position sensor are at fault ?

The pain is that the TM relay per my circuit diagram is a non-serviceable items and thus requires a new relay/fuse box at $6-700.

Any thoughts to help me determine if it's the relay/fuse box or Throttle body that I ought to replace ??

 

TPS is usual cause of limp mode and if that does not solve it replace fuse box

with used one.They are available and not expensive.

NB fault code is pointing at TPS.

I have dismantled my spare fuse box to look and replacing non serv. relay is not easy.

I have photos but will not upload-e mail me for photos if you wish

robatmeirion@gmail.com

 

My experience. Limp mode every week. After changing throtle body, two years nothing. Why ? Sensor of TB is bad, position of sensor is not defined and system don´t know, what happened. The resolution is send the car to limp mode.

 

I had this problem a year or so ago and it turned out to be the battery. Battery seemed fine-never failed to start the car but it tested bad at the dealer and they replaced it. Fixed the problem.

 

FYI, battery was replaced in April with genuine Jag battery from local dealer that I installed.
This problem appeared after a long stop and go run on a hot summer day.

I am planning to replace the TB shortly, We shall see what change that brings.

 

Replaced TB, engine now runs without limp mode !

However it is running roughly and continues to display "engine system fault, dsc not available and park brake" on the dash, has both red and amber lights.

Tried to reset the codes/CEL with my generic code reader, also
Disconnected the battery for 5 minutes and tried again, same result, as above.
code reader still reads P1000 and P1251, fault codes.

Given that the car runs and pressing the accelerator gives normal but rough response I think that the TM relay is probably working, so why the codes, messages and lights?

Is it that my generic code reader (sears innova) cannot effectively reset the ecm?
Battery reads 12.26V, and when engine runnig it is charging at 14+V

I would appreciate advice on next steps.

 

P1000 is not interesting, that is only message,that self test of car wasn´t ended.
P1251 :
· Throttle motor relay coil power supply circuit; open circuit
· Throttle motor relay failure
· Throttle motor relay coil to ECM circuit; open circuit
· ECM ground circuit fault (relay coil drive)

Try disconnect battery OVER night, 5 minutes is not enough. And maybe You need another reader.

Jag had this problem in very hot areas (near East):

"Investigations have determined that for the markets listed above, extended idle periods in very hot ambient climates with the air conditioning in operation, can cause the throttle position sensor
to fail resulting in diagnostic trouble code (DTC) P0121 on vehicles up to 2005MY or P2135 being stored on 2005MY vehicles onwards, with the vehicle going into limp home mode and the restricted performance indicator lamp displayed on the instrument pack.

Resolution:
You are requested to replace the throttle body at the next available service opportunity."

The battery must be before clinical death for limp mode.

Hi Roman

 

I replaced the TB and removed the battery for 2 days and charged the battery to 100% using a "batteryminder plus" charger.

Result: engine starts up and runs roughly, out of limp mode (it will rev to 2500rpm)

I then reset the CEL and turned the car off. Waited 2 minutes and then started it again. Same fault messages appeared and code read resulted in P1251 again ! (car is still idling rough, out of limp mode).

Any suggestions please.

 

Possible fix here:

https://www.jaguarforums.com/forum/x...51-code-44082/

 

I haven't read anywhere here anything about the three front earthing points. These are just behind the headlamps on the bulkhead by the radiator and can corrode badly and cause all manner of funny symptoms.

Suggest these are at least checked out, and confirmed OK and not corroded. FWIW I check mine regularly, You ave to remove the radiator top cover first. It's worth a shot anyway.

 

Note that the ground studs are aluminum and are basically riveted to the body, so they are easily broken off if over-tightened, which has happened to several members. The torque specification is just 6.5 lb.-ft. / 9 Nm, so take care....

Cheers,

Don

 

I replaced front fuse/relay box with a used unit and swapped my good relays/fuses into it.

Car has worked fine since and passed state inspection.

HOWEVER, I now have a passive battery drain after shut down !

After shut down and 45 minute wait, battery drains at 3 amps !

I hope be running that one to ground in the near future.
Could it be the replacement fuse/relay box ?