rangerovers.pub
The only place for a coil spring is up Zebedee's arse
Member
Joined:
Posts: 14

My 98 P38 4.6 HSE started this past Spring acting up in regards to hesitancy in shifting into gear from Park. I had gotten "gear box fault" messages occassionaly on the screen, but it always ran like a champ. Soon, it began to not react out of Park and I had to roll about 4 feet before it would engage, then eventually keep the truck creeping at intersections in order for it to shift properly and go. If you stopped, you were sunk and then had to use reverse. It made it interesting to say the least to drive through crowded intersections etc. The truck only drives in limp mode (3rd Gear) with the TCM disconnected and with it connected, but with intial hesitancy after the engine rpm's are up at 2000 then it moves slow and is fine in 3rd. I tried a different TCM to no avail. The engine runs smooth and there are no 3 amigos, only 2, the ABS and TC along with sister Check Engine light. Codes captured: P1775, P1777, P0722, P0740. I checked out the wiring to the transmission and the connections. Should I change out the XYZ switch? What do you guys (Experienced and Wise Ones) think? Thanks for your thoughts in advance

Member
Joined:
Posts: 981

You have diagnostics to pull the error codes off, so thats a good start - if they are landrover specific diagnostics (Nanocom/Hawkeye etc) then you should be able to see the xyz switch outputs (Nanocom can definitely show this, not used Hawkeye to confirm if that does). The corresponding table of outputs for gear selected are shown in RAVE so this should let you confirm if the switch is good or suspect without swapping the switch out. Theres little point swapping it if the switch appears to be ok (and usually when they fail, it starts intermittently and will clear on subsequent attempts rather than failing outright). You won't be able to do that with an off the shelf universal obd reader though.

It might also be an idea to scan the gearbox if you have suitable diagnostics to do so?

All the fault codes point towards electrical faults with the gearbox itself (solenoid faults mostly it seems). usual failure point for those is corroded connectors, so when you say you have checked out the wiring have you pulled connectors apart to check they aren't rotting inside where water has got trapped in them? checked with a multilmeter? Those more used to the p38 will probabbly be able to tell you which connectors would be the advisable ones to look over.

Member
avatar
Joined:
Posts: 6228

The XYZ switch drives the LED next to the gear lever and also the gear display in the dash (although this will usually blank anyway if the gearbox is in limp mode), but if the LED next to the gear lever displays correctly, then the XYZ switch is fine.

The only time I have know an auto hesitate before engaging gears, was on an Audi where somebody had filled it with the wrong fluid. It was one built at a changeover point so the fluid was correct for the year of car but not the particular gearbox fitted. I assume you have checked the fluid level as per the book, checked cold with engine running in Neutral after slowly cycling through all the gears. Is it the correct fluid? It should be Dexron 3, not Dexron 4 or 5, later is not always better and isn't an upgrade as many seem to think.

Member
Joined:
Posts: 14

Thanks guys, I will check again and look at he connectors thoroughly and check into what you both suggested. For clarity; this scenario started gradually with the truck hesitating from Park into Drive, then it eventually had to roll a few feet before it kicked into gear (Drive). I had to creep at stop signs/lights and if was moving slightly it would shift out fine. Eventually, it was "no go", unless I cleared the computer by removing battery terminals and touching together. Finally, instead of dealing with that nonsense, I wanted to move toward getting it fixed as I waited for my mechanic who has me several weeks out. I appreciate the insight. :)

Member
Joined:
Posts: 296

Removing the battery terminals and touching them together, unfortunately is a myth with P38s, it doesn't actually do anything.

Member
Joined:
Posts: 14

Yeah, I figured as much with the battery cables - also, the issue started before I had the fluid and filter changed, and I see lights by shifter...

Member
Joined:
Posts: 14

(https://www.landyzone.co.uk/land-rover/range-rover-p38-hse-4-6-1998-gearbox-fault.320680/) this is very similar to my symptoms...

Member
avatar
Joined:
Posts: 6228

Very similar problem but unfortunately no resolution other than he changed the gearbox. That would seem to point to an internal fault within the gearbox but even then it could have been electrical and he disturbed the bad connection when changing the box. From the codes, 1755 and 1777 refer to the interconnection between the engine ECU and gearbox dealing with the ignition timing retard but the others are interesting. P0722 is the output speed sensor, while P0740 is the torque converter clutch so both electrical. However, electrical faults tend to work or not, not appear and gradually get worse. A few posts on the subject (it seems to be common on Discoveries fitted with the 4HP22 gearbox) on other forums have mentioned battery and alternator but I can't see that either, unless the supply getting to the gearbox is low due to a bad connection somewhere.

Member
Joined:
Posts: 981

It might be worth checking your battery voltage on startup and for the first minute or so of running. I didn't get the fault codes you have, but did have issues with a lack of drive for a few seconds from startup when I discovered the voltage coming out of the battery/alternator was dipping down to around 9v. Was a problem with the 12v pickup (not the charge cable the other little cable) in my case, correcting that stopped the lack of drive happening from then.

Member
Joined:
Posts: 1157

If the problem isn't as simple as battery voltage are there any multimeter tests he can do to see if the TC clutch, output speed sensor, etc, are electrically working (even though this wouldn't necessarily prove they were mechanically working)?

I don't know the P38 boxes as well as many here but such problems on other gearboxes can be due to bad electrical connections such as the connector between the box and vehicle loom or internal on the valve body. Sometimes breaks on electrical tracks on the valve body can be a DIY repair.

Is there a common component that could go bad that could cause all these reported problems? For example on other boxes you can expect to get codes for certain speed sensors if a clutch is slipping or not engaging due to a bad solenoid, in which case you get the code for the solenoid but you also get a code for the speed sensor. If there is a possible inter-relation between codes it points toward an actual gearbox fault, if there is no possible inter-relation it could point more towards a generic electrical problem such as a bad earth or as Bri said battery voltage.

Member
avatar
Joined:
Posts: 6228

The box is a ZF 4HP24 (with the almost identical but lower power rated 4HP22 fitted to the diesel and 4.0 litre P38 and Discovery 2) and it's also fitted to quite a few BMWs amongst others as well, so pretty common. So you may have come across it before and not realised it is the same.

Member
Joined:
Posts: 981

There are circuit diagrams in the ETM section of rave which give quite a bit of detail, but don't run you through point by point tests of components (Which some other manufacturers documentation such as Ford TIS does).

The connector C559 carries both the lockup solenoid and output shaft speed, located under the centre console (there are photos on rave of both the connector and location of all the connectors like that). It may be worth a look at that given both feeds go through it. I'd really suggest a good look through the circuit diagrams might be an idea to start with, and as it says in the ETM look for the common points if you have multiple faults appearing to see where those bits join up.

There is a post on the top of the forum here with a Rave download if you don't already have it.

But check the battery thing listed above first as its much easier to rule out!

Member
Joined:
Posts: 296

This may help. ZF HP4 22 + 24 Manual

Member
avatar
Joined:
Posts: 6228

Not sure that is going to be much help as it's for the earlier 4HP22/24 as used in the Classic rather than the 4HP22/24EH electronically controlled boxes used in the P38. So if it is a mechanical or hydraulic problem the manual may be of some use but if it is an electrical problem, as we suspect, then it doesn't even exist in that manual.

Member
Joined:
Posts: 296

This one might be better then, in combination with the first link.

Range Rover 4 Speed Automatic Transmission

Member
Joined:
Posts: 14

Man, I wish you guys lived near me... I'll check to the best of my ability on those listed potential solutions. I need a lift so that I can stand and work under the RR. I have a vertigo issue when I lay down a certain way with my head angled (old soccer goalkeeping injury). Anyway, the battery is 12.4 volts stand alone, 13.4-13..7 when truck is running and 14.1 at the alternator. I have Rave too. Thanks again everyone, you're remarkable.

Member
Joined:
Posts: 380

Marshall, you're the man! Thanks for the useful links! :-)

Member
Joined:
Posts: 14

Transfer Case Motor? what does it do exactly and can it be the culprit?

Member
avatar
Joined:
Posts: 6228

It's the motor on the transfer case that changes it from high to low ratio. You can see it bolted to the back, next to the parking brake drum. Looks much like a windscreen wiper motor (and is actually very similar to a windscreen wiper motor. I drove a car with the motor unplugged and that gave a permanent Select Neutral message on the dash and didn't allow the torque converter to lock up so it was revving higher than it should when cruising. So although interconnected with the gearbox, I don't think it is likely to be the problem.

Member
Joined:
Posts: 14

yes, I checked it along with the connection - hmm... isn't there a sensor inside the valve body that is connected to the shift solenoids?