Lotta info here, so feel free to skim (or skip)...

So, I was driving up to pick up my son from college yesterday evening and I had the "Gearbox Fault" light come on and I'm looking for some guidance on the best way to approach the issue. It's a 2004 XJ8 with 157K miles. I bought it last summer from a fellow forum member who had replaced the transmission fluid and filter at around 140K.

Here are the details of what happened... I was about 2 hours into a 2.5 hour drive and I was on the interstate and accelerating to pass a somebody when the amber light and "Gearbox Fault" showed up. The car seemed to be stuck in gear (either 4th or 5th) because the tach was between 3000-3500 rpms and I was going about 55 MPH. I drove that way for about 20 minutes or so and got off on the first exit, pulled into a parking lot, and plugged in my scan tool. The only TCM code was a P0730 (Incorrect gear ratio) DTC. I cleared it, picked up my son and returned home driving GINGERLY the whole way without any further DTCs.

I've read the ZF sticky and done some generally research. I assume that driving it around and hoping the error doesn't return is a bad idea, so the car is parked in the garage for now. My plan is to drain the transmission and look at the condition and quantity of the fluid and go from there. However, any advice on how to proceed is greatly appreciated. I have very little A/T experience, but I'm willing to put some time and effort if it means fixing the transmission without spending a ton of money.

 

What is the age and condition of the battery? A failing or weak battery can be the source of many electrical 'faults' that crop up.

With the ignition in the OFF position after five minutes, there should be a minimum of 12.5 volts across the terminals. If not, you should most likely replace the battery.

Another condition that can cause the 'Gearbox Fault' message to appear is misfire(s) caused by deteriorating coil unit(s) that won't always turn on the MIL and set a DTC.

 

The PO installed a new battery not too long before I bought the car, so it's fairly new. He replaced also the spark plugs as well chasing an abrupt shifting issue and seemed pretty satisfied that fixed the problem at the time. I'm not sure if he replaced the coil packs though.

It's really done pretty well up until last night, except for the occasional clunky shift, but I don't drive it on the interstate very often.

Edit: Is there a way to diagnose the coil units?

 

It would be wise to have the battery tested rather than throw parts at the problem. The battery is easy to test and then you can eliminate that as a source of the issue before going any further.

I also suspect coil pack(s) misfire, so after a cold-soak, you can remove them and see if there is any oil fouling or other deterioration that can cause a misfire. You will get the 'Gearbox Fault' warning due to misfires when the TCM goes to limp-mode to protect the gearbox.

 

Hi electechbw,

You can download the full X350 Diagnostic Trouble Code Summaries guide at this link:

Jaguar X350 DTC Summaries

According to the manual, the primary possible causes of the P0730 DTC are an ECM torque signal fault, or transmission mechanical failure. The manual suggests driving the vehicle from a stop to 70 mph, then confirming that 6th gear is engaging by moving the gear selector to the 5 position and observing that the transmission downshifts (the tachometer should indicate higher rpm).

The torque signal is communicated via the CAN between the ECM, TCM, IC etc., so it is possible you may have one or more network-related DTCs flagged (U-prefix codes), but to read them requires a diagnostic system capable of scanning the proprietary Jaguar codes. It might be worth finding a forum member or local shop with the Jaguar SDD system or a high-end third-party system such as AutoEnginuity with the Jaguar enhancement to scan your car to see if any additional DTCs are flagged that might help with the diagnosis.

Assuming the fluid is correct (Lifeguard 6 or Mercon SP) and the level is correct, it is possible the fault is electrical. The plastic sleeve around the electrical connector on the transmission is known to develop leaks that contaminate the connector pins with transmission fluid. It might help to clean that connector with zero-residue electrical contact cleaner, along with other connectors and grounds associated with the TCM and engine management system (EMS). You can download the Electrical Guide here:

Jaguar X350 Electrical Guide 2004

It is also possible that the issue might be resolved by having a Jaguar dealership clear the adaptations in the TCM and update the TCM firmware to the latest version available. Some independent Jaguar specialists may have the ability to do this. One of the versions of SDD I have has this capability (v. 131.03, I think), but to do it safely requires a rock-stable OBDII-to-USP interface such as a genuine Ford VCM, Drew Technologies Mongoose, etc., along with a proper high-amperage power supply connected to the battery, such as the Jaguar-specified Midtronics PSA-550 (50A of low-ripple DC at 13.6V).

I also agree with NBCat that you should have the battery checked on a proper diagnostic system. The age of the battery is irrelevant if there is a problem in the charging system or the battery is aging prematurely because it is of a type that is unhappy with the higher charging voltages generated by the X350.

All that to say, it is not impossible that something is amiss inside the transmission, such as a sticking solenoid, a worn clutch, etc., but it's worth ruling out other possible causes first.

Cheers,

Don

 

Thanks, Don and NBCat. I appreciate all the info. I have a real Ford VCM and JLR V118.5, so I may look into get a battery maintainer and flashing the TCM. I'll definitely check the battery and the condition of the coil packs before I do anything too drastic.

 

With SDD you may need to select the routine that is called something like, "Read all fault codes including unrelated codes," in order to see all the codes that are flagged for all systems and not just those related to whatever symptoms you entered to begin the SDD process. It would be worth knowing if there are additional codes that might help narrow down the diagnosis.

Please keep us informed!

Cheers,

Don

 

30A minimum for the battery maintainer.

The higher amperage the better. I use a 100A battery support system. I dial it to 13.6V and forget about it.

SDD looks for 12.8V or higher voltage before allowing flashing.

 

So, I haven't had a ton of time over the holiday weekend, but I did a get a chance to check a few things. Here's what I found:

1. Doing the battery test posted above, I found the battery was at 12.8 Volts after 5 minutes and 12.7 Volts after 30 minutes. The charging voltage with the engine running was 14.9 Volts.

2. I have pulled off all the ignition coils yet, but I decided to use IDS to look for any codes and what I found was a huge list of DTCs. A couple of which were misfire codes. (See attached)

3. IDS couldn't communicate with my ECM. The error kept returning no matter how many times I tried to re-establish communication. (See attached).

I'm assuming not being able to connect to my ECM isn't good. Is it possible that something got corrupted and I can reset the ECM or something?

 

Those look like historical data, maybe from when the previous battery went low. My IDS readout looked a lot like that when I had battery trouble.

Do you have the battery green light on the IDS screen (bottom RH corner)? If not there maybe an issue with wiring harness connectors and/or grounds. I had a campaign to check wiring harness connectors ,clean them and seal with silicone grease. Also did a similar campaign with grounds.

 

Yes, the battery light is green in IDS. Along with the battery problem, The PO also had some grounding issues from a corroded grounding lug in the engine compartment, which he repaired. So, it's very likely that many/most of these are codes related to problems that no longer exist. However, I'm not sure how I can tell which are relevant and which aren't, at this point. Now that I have a record of them, I'll probably just clear them all and see which come back.

 

I did exactly that after saving the information.

 

If you have misfire codes, these can cause thesecgearbox faults and error codes such as incorrect ratio.
THIS DOES HAPPEN WITHOUT NECESSARILY ANY ENGINE MISFIRE CODES TOO.
I would suggest a new set of coils, especially after 100k miles.
These are 4 wire coils, ground, supply, trigger and misfire.
coils sense a misfire, or if faulty, tell ecu of misfire, and interupt gearbox changes.
A set of 8 coils can be had on ebay for $120, one original is $120.

​​​​​​See also the sticky at the top on ZF transmissions and the errors a cracked spark plug gave.

 

I had a bad rear left ABS sensor that gave intermittent faults with ABS, Traction and Cruise faults, then started throwing up a Gearbox fault as well, the ABS sensor is a speed sensor, so it must have been sending false info to the transmission ECU as well as the engine ECU and causing ghost faults to appear, that's when i replaced it. not had a problem since.........

 

Just a quick follow up. The battery seemed okay (as I posted earlier), so I decided to clear the TCM adaptations and then reflash the ECM and TCM. I also noted, then cleared the majority, of the DTCs. I didn't do anything with the trans fluid.

I took it for a test drive and I shifted from 6th to 5th per the instructions in Don's post. It downshifted smoothly, but with a slight delay (maybe a second or so). I'm not sure if that's normal or if it's a possible concern. Anyway, I guess it's wait-and-see at this point.

 

We did practically everything we could as suggested in this thread. Does anyone have a suggestion on what else to do, replace or maintain the car's condition back to its default to No gearbox faulty state? We are at our witts end at this point.

 

Hi Jaggiegal,

What are the diagnostic trouble codes present in your car, including all of them, even those not apparently directly related to the transmission?

Cheers,

Don

 

P0782, that's it. Ty

 

Hi Jaggiegal,

Assuming your Jaguar is an X350 or X358 (an XJ built from 2004 to 2009), here is the definition of P0782:




The most common cause of transmission codes like P0782 is oil contamination of the transmission electrical connector due to failure of the connector sleeve seals. The connector, which is on the rear end of the transmission, can be disconnected and inspected for oil contamination. The sleeve is replaceable, but the transmission oil pan/filter assembly must be removed for access to the sleeve locking latch handle.

A short-term fix is to flush both halves of the connector with a zero-residue solvent such as CRC QD Electronic Cleaner spray.

Cheers,

Don

 

I would check the earths, my dash lit up like a christmas tree when one fell off.