Was returning from a trip with the beast ('01 XJR drive train in a Mark 2) when 2 blocks from home I lost throttle control and the engine started missing and surging. The message center flashed Traction Control Not Available, ASC Not Available and Engine Failure Mode along with a red telltale. Fortunately I made it into the garage where my scan tool is showing DTC 1229. In searching this it looks like all of that messaging is triggered when the ECU throws that trouble code. Clearing the code and a hard reset had no lasting impact - the beast starts right up with a high idle (2000 rpm), slowly settles to a normal idle then throws the code and messaging along with stumbling and surging. Some years ago Moderator Don B posted Pinpoint Test T for P1229, so I'll start there - it looks like either a connectivity/circuit problem, a bad throttle motor relay or a bad throttle motor. Let me know if I'm on the right track and what the most likely problem might be. I see lots of discussion about replacing throttle bodies or having them rebuilt - hoping that's not where this is headed. I think we're around 87k miles on the engine. Many thanks.

 

I found this from a forum member that might be useful:
"I wanted anyone who may have a similar problem with the P1229 code
on my 2000 XK8 to know I found the problem. (See my previous post)
I spoke with a friend with a Volvo who had very similar problems.
He recommended to do this as it fixed his problem. I disconnected
all the electrical connectors I could find under the hood and
cleaned each one with ‘electrical contact cleaner’ and reassembled
by pushing them on and off a few times to clean any corrosion that
may have accumulated. Today I drove the car for two hours. No
light. No failsafe mode. No problems at all. Since I was getting
the ‘failsafe mode’ several times, shortly after driving the car,
and having cleared the code each time, I feel confident the problem
has been resolved. A Jag mechanic told me that small amounts of
corrosion can cause false codes to appear and simply by cleaning"
them the problem may disappear."

As these ladies age, we may see more and more of this our cars.

 

Will certainly check/clean all the critical connectors I can find - thanks.

 

P1229 focuses on the Throttle Motor so I would first check/clean its connector - the round 2-pin connector on the throttle body.

 

Unfortunately the simple fix wasn't the problem. These connectors are nicely engineered with O-rings and positive locks - like new inside. I'll do the pinpoint tests to see if I have a wiring problem. Does anyone know if there's a way to test the throttle motor itself? I'm assuming with this fault the ECU is taking that circuit off line so it's not possible to use live data to read the Throttle Position Sensor.

 

Fortunately the next simplest fix was the problem. I swapped the ac compressor relay for the throttle motor relay and the beast is running fine. In all my years of working on cars I can't remember ever replacing a bad relay. Thanks again for the help with this.

 

You will, no doubt, find that relays on these cars are frequently the problem.

 

The A/C compressor, starter motor and fuel pump(s) are the most frequently failed relays in the system due to the high amperage and useage. I’d highly suggest taking the rear fog light relay in the trunk fuse box in place of your “new” throttle body relay.