1998 XK8.

The horn went out and the steering column refused to go up or down so I went and had a look. In the process of tracing power, fuses and relay, something melted down. I didn't do anything abnormal or make contact with anything I should not have.

Upon turning the key in the ignition I discovered that the vehicle went into Engine fail safe mode, transmission fail safe mode, incorrect part, and the climate control unit beeps and displays an ERR message before turning on. I cannot even get the starter to turn or the windows up.

I checked all the fuses on the car and they are good. All the relays that need checking "appear" to be fine with no burn marks but I haven't had the time to test them.

Initially I could not get into the ECU or Trans control module but I could read other things with the key in the on position. Now the OBD reader will crash if I turn the ignition on to the on position and I can only read codes from the body module.

For a number of reasons I assumed the Body control module had crashed even though it communicates. I have a spare 98 module on hand that is known to be good. The swap made no difference.

Also, under engine identification I get readings FFF for the ECU and FFFFFF for transmission.

Lastly, I cannot get into the instrument pack to read anything.

Anyone?

 

Well . . . welcome to the forum . . .

. . . something melted down?

YOU LET THE SMOKE OUT OF THE WIRING HARNESS! Obviously need a smoke reinstall kit.

No blown fuses?

Perhaps a hard reset for lack of any other suggestion.

 

What is your battery voltage reading?

There are three monster 250 AMP fuses on the floor of the trunk (under the removable floor) in the rear....check that they are all OK.

 

Battery voltage was bad and that's why the OBD read crashed when I turned the ignition on. The battery is now back in good health.

Mega uses check out as well. I never knew those were there.

I'm beginning to lean toward security system failure but the problem is I can do anything about it.

 

The non start/transmission fault/incorrect part issue was simply the Positive Ignition Relay.

However, I still cannot get into ECU and BPM with any OBD reader and the horn still doesn't work.

I just need the horn to work so that I can pass inspection. Is there a way to diagnose this? So far all I've come to know is that I need a certain program to check it out.

 

In the engine compartment fusebox (left side of car) check fuses 11 and 13. If they are OK, check relay #6 in the fusebox. Also check fuses 5 and 7 in the driver side of the dash fusebox.

You can pull the relay and short pins 3 & 5 on the socket (the pin numbers are on the relay bottom)...that should activate the horn. If that works, then the relay or relay drive is bad. If not, it is a problem with the horns or wiring to them.

If it looks like the relay or relay drive try swapping with another relay in the box. If it still does not work, then it is probably a steering wheel switch a clock spring or BPM problem. Check this by seeing if you get 12 volts to drive the relay between pins 1 and 2 of the relay socket when the horn button is pressed.

 

Common problem with a lot of US cars is that the cigar lighter (power port these days) and the OBDII data port are both powered off the same fuse. Blow that fuse, and it is easy to do, and the diagnostics no longer work. The Jaguar data port B+ supply is from the driver side fascia fuse panel, fuse 13. That may fix the code readers.

The horn fuses are in the left engine fuse box, fuses 11 and 13 as a place to start but steering column wiring is the next place to look.

 

Thanks for the information. All fuses and relays for the horn are good. I know I have the power going from the BPM to the horns because I can set the alarm off with the remote. So technically half of the horn system works. Based on the wiring diagram the fault is between the Horn switches and the BPM.

Test point, thanks for the notice on the cigar lighter/OBD II circuit. I'm pretty sure that fuse is blown. I'll check in on it.

I have a feeling I'm going to have to get into the column wiring for the horn answer.

 

Pinned out the BPM and it got no signal from the horn. Ohmmed out the line and can up with nothing. Evidently the PO had work done to the car because half way down the harness under the driver side the wire for the horn ground was cleanly cut.

 

May I make a suggestion. When you guys mention drivers side. Please identify which drivers side. There are two.

 

You have to go over to the right top to see location . . . that's a good clue.

But it is a wonderful idea to fill out the location and include the MY/XJ8/R information in somewhere in your profile.