OK - I'm in need of a little expert help. My heated seats and steering wheel seem inoperable (2009 XK convertible). I turn them on in the usual way, the display reacts properly (as though they are on, I can adjust the seat heat level, etc), but no heat. Maybe the tiniest, barely preceptable bit of heat - but essentially no heat in the seats or the steering wheel. I assume they should warm up noticeably, but this is my first Jag - so let me know if they are just known for *really* (and I mean *really really*) anemic seat / wheel heaters.

I removed both seats to get at the connectors, turned on the seat heater on the dash screen, and measured the voltage across the supply for the driver seat (connector DS001, pins 1 and 11). I got 9.5 volts. I then did the same thing on the passenger side and it flashed 14 volts for second and then went to 9.5 as well.

First - note that in order to measure the voltage, I had to disconnect the connector under the seat, which also disconnects the seat heat sensor.

So - my first question is this: given that the seat heat sensor is also disconnected, should I expect something different than 9.5 volts? Or is 9.5 volts a smoking gun?

I thought I'd trace the wires back to the central junction box to find connector CA015 and measure there. That is listed as being at the base of the driver's side A pillar. I removed the dash end panel (the plastic triangular-shaped panel) but did not see the junction box nor the CA015 connector.

So - my second question is - can someone point me to where that junction box is located so I can find the CA015 connector?

And finally - my third question is - .... any overall advice? The electrical manual is silent on how the sensor is fed back into the heating circuit to moderate the seat temperature. Is there a control unit somewhere that manages that? I could not figure that out from that electrical manual. If you can point me to a document that explains that - I'd be very appreciative.

Thanks so much everyone! All the best - Murray.

 

Quick update - I believe I found the CJB in the workshop manual - behind the panel the hood release is on - near the drivers left foot. So I am good with my second question, above.

Thanks!

 

Did you find this in the workshop manual?

Seat Heaters
There are 4 seat heater settings available; Off, 1, 2 or 3, which can be set through the TSD. The heat setting is relayed to
the vehicle occupants through a graduated display on the TSD.

Operation of the heated seats is controlled by the Automatic Temperature Control module. When the ATC module receives a heating request from the
TSD, it broadcasts a message to the CJB over the medium speed CAN bus. The CJB then provides a hardwired 12 V supply
to the 3 heater elements contained within each seat. The 3 heater elements, 2 in the seat cushion and 1 in the seat
squab, are wired in series.

The ATC module monitors seat temperature using a temperature sensor located in each seat cushion. The CJB provides the
temperature sensors with a 5 V supply. The level of the returned voltage back to the CJB is proportional to the seat
temperature. The value of the return signal is broadcast to the ATC module over the medium speed CAN bus which it then
converts into a temperature value to allow it to control seat temperature to the required level.

The ATC module will suspend or disable operation of the seat heaters if any of the following occur:
Battery voltage exceeds 16.5 ± 0.3 V for more than 5 seconds. Seat heating is re-enabled when battery voltage
decreases to 16.2 ± 0.3 V

If a short or open circuit is detected

If the seat heat temperature rises significantly above the target temperature setting.

The graduated display on the TSD remains illuminated until the seat heaters are turned off or the engine stops. If the
engine is restarted within 30 seconds the seat heater resumes the previous heating level.

Steering Wheel Heater
The steering wheel heater has 1 heat setting and can be turned on and off by pressing the soft button located on the seat
heater TSD screen. The on/off status of the steering wheel heater is relayed to the vehicle occupants through the TSD.
When the ignition is switched off, the heater will reset to off.

Power for the heater element is supplied by the CJB on receipt of a request from the ATC module over the medium speed
CAN bus. Temperature control for the heater element is provided by the steering wheel heater control module which
receives a temperature feedback signal from a NTC thermistor located within the steering wheel.

 

Thank you so much! Yes - with your help I did find the diagnostics course content and the manual with these passages and with the diagnostic information.

Based on this, I think I will have to throw in the towel on at least the diagnosis part. I think what I need next is a code reader to see if any of the listed diagnostic codes are coming up. I'll take it in and pay for a diagnosis and see what they say!

Thanks very much for the assistance!