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So having sorted the throttle body I'm back for more in my quest to get zero codes.
I have two gearbox codes, I think probably unrelated but possibly not:
Symptoms are slightly jerky/harsh gear engagement from Park, car not on the road so haven't tested shifting when driving. Doesn't go into limp mode at least not while driving around you land at say 10 or 15mph and no selector lights.
So far I've been through the J gate and found the selector disc in pieces so not pressing the top D4 microswitch when going from D to 4 and the neutral microswitch missing it's lever and the actuator button broken, new switch and disc on order old one glued back together for testing.
I also have no gear selector lights. The red P illuminated very briefly prior to me removing the rotary switch but as soon as you moved the cable so much as a fraction of an inch it went out and would't come back on when you shifted back to Park, this the same with engine running or not. after removing and replacing the rotary switch no lights at all.
Research led me to think this was a faulty rotary switch causing the 706 and something else the solenoid one (I have the later black switch on a '98 so it may have been replaced already?) I've checked the engine bay connector and the switch loom based on the below and get exactly these results with virtually the same resistance in all terminals when in drive/park/reverse etc
This makes me think the switch is maybe ok. But then I have no selector lights so maybe the connections break down under load?
Next checked the TCM connector, seems good and bright, opened it up anyway no evidence of any burning or shorts on the board.
Checked continuity/resistance as per technical manual with all the pressure and solenoid readings at the TCM connector within range, was hoping number one might be off as I think that is the low one that reduces clutch engagement from park?
Engine bay earth is clean.
Checked 16 pin transmission connector on the trans, looks very clean with a good solid earth there too.
Tempted to take the switch apart but I see how much secondhand ones are and that the company that repairs them won't take one if it's been played with so maybe I just send to of to make sure for the sake of £65.
Getting to the point again of running out of things to check.
I know I should check the cable adjustment but it seems to sit exactly where it should and goes into gear in the right places.
All of that said I am ready to be enlightened by your expert wisdom!
Last edited by SpannersNK; Aug 17, 2025 at 02:39 PM.
Ok that's interesting so Icarsoft's code description is a bit misleading for the 1745 at least. Will look into the no 1 pressure regulator more closely.
The 0706 at least does still point to the rotary though but I will double check the cable and the D4 as well.
Data logging would be helpful here I think but the live data in my Icarsoft reader doesn't go as far as showing what the switches are doing (unless I'm missing something)
The D4 switch is usually faulted when people use the J gate to downshift/upshift and the switch is faulty, falls off the mount or the cam disc is broken.
The pressure regulator readings can get skewed if the windings are out of tolerance or metal filings from worn parts get into the connectors.
I had the same faults with one of my ZF 5HP24 gearboxes so I just transferred the whole set of electric actuators on the valve body from another gearbox.
The other box had mechanical issues but the electrics were good.
The resistance through all 5 pressure regulators was virtually identical within a couple of tenths so hopefully that is a positive but the car has been sitting in storage for 8 years, not driven much for the previous 5 either so maybe a fluid and filter change would be useful. I'm never quite convinced by the sealed for life thing.
The D4 cam disc had split so I'll double check the switch is still working, it looks and sounds fine but I'll check with a multimeter and get the rotary switch rebuilt.
So a week later and I've just fitted the rebuilt rotary switch courtesy of S & H services on Ebay, £65 and a quick turnaround, a nice job and it's fixed the 0706 fault. I have gearbox selector lights now also but this was probably in addition to the rotary switch due to 7 of the 9 connections on the J gate board being broken. I suspect they were just making intermittent contact causing the flaky indicator lights. I removed the connector pins and soldered the wires direct to the board and replaced the illumination bulbs.
The broken neutral switch was replaced too with an identical 3 quid microswitch from Amazon.
I still have the 1745 fault though, I realise this is Pressure reg 1 circuit malfunction not a solenoid. OBD doc shows causes as:Transmission to TCM pressure regulator 1 circuit open circuit or short circuit - I have checked the resistance from the TCM connector for all 5 and they are all within the 4.8 - 6.8 ohm range, being 5.6, 6.1, 6.0 and 5.9 also the live data(engine running) shows the calculated output for all 5 as 0.15A not sure what the A refers to but it feels if I'm getting measurements and the same across all regulators it can't be a short or open circuit?
Transmission internal pressure regulator 1 circuit open circuit or short circuit - same as above
Pressure regulator 1 failure - could it be this? Would that give a circuit malfunction code but test ok?
Is the next step to just fit a new regulator? I'm going to change the oil and filter so that would be a good time to fit a new one.
I haven't driven the car on the road so don't know how it actually effects drivability maybe I should do this first. The OBD doc mentions it will go into limp mod but this isn't showing on the dash (would it show until driving?)
The code can be cleared and stays away until you shift out of park.
I am reading about the early version of this box having A-clutch drum issues but no reference in any post about it causing this code.
Obviously just one code now is better but hopefully it's not a biggy!
Last edited by SpannersNK; Aug 24, 2025 at 11:23 AM.
Just been reading about that, seems to be a popular fix/upgrade when there is a bit of wear or a step in the piston bore prior to the drum going. I will order one.
Having read far too much about gearboxes since last night would I be right in thinking that when the valve bore wears it allows fluid past the piston so the pressure regulator solenoid tries to compensate for that which increases the pressure more giving the clunky drive engagement and presumably the pressure reg error code is a symptom of that rather than the actual problem?
It seems there are two options, the TransGo if it's minimal wear and you catch it early enough, can't find any negatives on using it or the Sonnax reaming route if there is more wear and you have more cash (no idea how much the machining might cost). Or I guess a recon front valve body with that already done but I can't find a source for that.
So to wind up this thread for any future readers, all circuit/resistance checks for the solenoids proved within range. I removed the valve body and had it checked by an amazing chap who hangs out on this and teh Range Rover forums, he's an absolute guru with these boxes and checked everything with a fine tooth comb. Very little wear anywhere and a lot of new parts fitted in 2005 ish, one solenoid a fraction out of his tolerance so he replaced it anyway, Put it back in the car and still had the gearbox fault.
Rechecked the harness, earths and transmission module and all checked out. This only left an internal non-visible fault with the control unit. £22 later and an Ebay replacement went in and the fault went away never to return.
1745 Low clutch timing - 0706 Transmission range
