www.jec.org.uk

Hi All

Please can you help me? I'm new to the forum.

I have the above Jag. When it's put on the Jag diagnostic machine it produces the following codes:
P0228 - Throttle Position Sensor C high input.
P0229 - Throttle Position Sensor C intermittent.
P1574 - Throttle Position Sensor Disagreement between Sensors.
1) Firstly which is Sensor C on the throttle body? Is it the large sensor at the top, middle front of the engine attached to the throttle body? Or is it the other electrical sensor on the throttle assembly which is at the rear of the throttle body and nearer to the bulkhead?

2) Is it easier to replace the Sensor 'C' by buying a replacement sensor? And does anybody know where I can buy a new sensor?

3) The Jag Indie that did the diagnostic said it was easier to buy a second hand throttle body with the sensors attached and simply fit the second-hand unit to the car with new gaskets etc.

I humbly look forward to receiving your views on the matter.

Yours sincerely - fitman207

Hi,

Firstly what alarms did you get that sent you to have an independent expert scan your car? amber light, red light or engine light illuminated, and were they flashing or permanently on?

The 3ltr V6 has a digital fly by wire throttle assembly, i.e. the accelerator pedal has 3 rheostats and the throttle position sensor (TPS) also has 3 rheostats. They talk to each other via the powertrain module (ECU). Partially hard wired and also by 2 twisted wires via a computer protocol. If damp gets into the accelerator pedal or the throttle position sensor then the comparison of signal from the three rheostats is different so it sends a fault code to let you know, but it may not affect the way the car drives.

Last year I had a similar occurrence with the accelerator pedal, I took it off the car (one wiring connector and 2 screws) and left it on top of the boiler over night, next morning it was fine and no intermittent red flashing alarms.

Having looked at my 2000MY 3 ltr S type the throttle body is at the very front of the engine in the centre and the TPS is on the front of the throttle body, with a wiring plug to its left (drivers side).

In your position I would mark the exact position of the TPS on the throttlebody (the 2 screws allow for some positioning adjustment) and remove it to the boiler top for the night. Otherwise You could contact 'Auto reserve' or another Jaguar scrap yard to see if you can get another to try.

I think that if you just substituted another complete throttlebody then you would have to have it set up by a Jaguar agent for the ECU to recognise it (not completely certain on that score).

I hope that helps.

Brian

Thanks for answering that, Brian.

I wrote an in depth article on the throttle body in the S-type pages which appeared in our May 2010 magazine. Essentially it is the same unit for V6 and V8 cars but the V6 unit has an anti frost flow pipe let into the body.

My car persistently went into limp home mode. Clumsy handling by the previous owner had broken a connection between the big black socket on the throttle body and the TAC Throttle Actuator Control module within the unit. No repair was possible. A ne unit is available from Jaguar for a very reasonable £1300 or remanufactured complete from BBA Reman at Rochester for around £500.

A sludged throttle throat and plate can cause issues. The plate is designed to snap to the shut position. A broken or weak spring or a throat and plate that are filth may inhibit that action and cause false signals to be transmitted to the control module. Clean out the throat first before trying anything else. A clean throttle also helps idle speed reliability. The sludge is from the part load engine crank case breather pipe which is fed into the inlet tract trunking. Clean the throat out once a year to prevent these and other peripheral issues.

Also try disconnecting the big black plug from the throttle a few times. Corrosion in that plug may cause the ecu to think that there has been a sensor failure. Sometimes that action is enough to restore full service.

I was fortunate to win an auction on ebay for a second hand unit for £20 including postage which came to me as in working condition. All I had to do was unbolt the old unit from the car, source a new gasket from jaguar which I now know is possible to make oneself and clean out the throttle throat and throttle plate with some rag and carburetor cleaner. That done, I cleared the MIL check light on the dash by disconnecting the battery for twenty minutes. I turned the key and the car started. I`ve done nothing more to that throttle body now, other than clean out the throat once a year. Reprogramming the car after a throttle body change is not necessary.

Before buying second hand, I would recommend finding your original part number from a defective unit. Annoyingly this is on the base of the unit and you can only get to that by taking the throttle off the car. It is essential to buy a replacement unit with exactly the same part number identification.

These throttles are built as one unit. Only the throttle position sensor mounted at the other end from the stepper drive motor can be replaced. The drive motor and TAC module are built and programmed to work together. It is not possible to swap out either of those two parts to repair. damage or defects to either the motor or TAC module means the unit is a scrapper. The only part that can be used again is the position sensor. That is not available as a spare part from Jaguar.

There are loads of these throttles around second hand. On ebay they sell for around £100. As Brian says, Andy at Autoreserve is a good second hand parts supplier as is Neville at North East Jaguar Spares and also Eurojag.

The throttle is one item that can have issues. The other unit often at fault is the throttle pedal which as Brian says can fail. One thing to check with the pedal is that the potentiometer on it is not damp. Sometimes removal of the pedal and overnight cooking on top of a boiler can cure an issue.

To quote from my article re the ways in which this system can fail....

"Loss of redundancy. ie, a failure of one sensor output. This causes the amber warning light to illuminate and the "fail safe engine mode" to be displayed on the dashboard message centre.

Cruise inhibit. Cruise control cannot be used.

"Limp home mode" in which a high idle speed is set with no pedal response to allow the vehicle to creep. The red warning light and fail safe message are also activated. this mode is set by the loss of two or more sensors".

A few pics here from the article. Changing the throttle is very easy. A few jubilee clips, four Torx head bolts and a gasket. should take no more than half an hour to fit. After that, clear the faults by battery disconnection, reset the clock and radio and away you go again.

Mike

30/03/14

Dear Mike and Brain

Thanks you so much for your much valued comments. I have printed them off and will follow the instructions.

Kind Regards - fitman207