Bongo Fury

Afternoon hive mind, bear with me while I recap.

Had an issue beginning earlier this year - HOLD light flashing, then not going into top once warm and >40mph. Code read as P0743 - TCC solenoid.
After much wailing and gnashing of teeth, put it into Royston's to have the solenoid changed, which he duly did about 10 days ago. He's roadtested, all OK. We pick it up, Mrs P gets down the road and the light comes on - same code. I take it up the road - no issue. Three times I've tried to clear the code.
HOLD light now comes on on engine start - code check shows P0743 AND P1521 (which is one of those 3 port valves on the vacuum system)
Took it up to the Quantocks this weekend, HOLD flashing, no top gear.
Did what we needed to do (foraging!) then went for some lunch at Kilve - no HOLD light at all, top engaging.
Had lunch, two mile down the road HOLD flashes, pull over, restart, good as gold all the way home.
This morning on cold start, instant HOLD light.

Question - does anyone know what inputs the ECU needs to see before it will power the TCC solenoid? Would a duff vacuum solenoid (P1521) on a cold engine limit the gearshift?

I'm running out of patience (and money!) with it now - Royston has checked all the continuity in the box, and the old solenoid was proving faulty, but I can't get my head round it now.

Will also share to the FB group just in case.

TIA
Colin

Hi Colin, I don't know Royston's , but the easy answer is take it back to Roystons ,if they have undertaken the work in the first instance, I would imagine it's up to them to finish the job.

The TCC isn't top gear, you have 4 gears + torque converter lockup. I would think the transmission is OK & the issue is on the vehicle, however I have no experience with the vehicle systems that control the transmission unfortunately.

Here's a couple of pointers from the Bongo Clinic on the main BF website:

Q: The hold light is flashing on my 1996 V6 Bongo. I’ve read elsewhere about potential problems with the gearbox and I’ve got a diagnostic code of 62 (shift solenoid valve). But before I invest in a new solenoid pack, which I can’t really afford at the moment, are there any other checks I can perform? (Tom from Truro)

A: Try checking the crankshaft sensor. If it’s faulty or even a bit dirty it can interfere with the timing of auto gearbox changes.

Q: I’m having problems with my gearbox. It doesn’t always seem to know which gear it should be in, especially at greater speeds. So, starting from cold, it changes gear OK, sequentially, up through the box without any particular clunkiness, and finally moves into top gear. However, if, say, I was then cruising along at 60mph in top gear and driving circumstances in front of me required me to back off of the throttle, with a resultant loss of, say, 15mph, reapplying the throttle would cause the gearbox to appear to be uncertain about which gear it should get back into. What’s the likely cause? And will I need to take it to a tranmission specialist? (Andy from Battersea)

A: Identifying and fixing auto-box problems can be time consuming and expensive. So before you go down that route try the following. Not all gearbox problems are actually gearbox problems at all. Lots of things affect when the gearbox changes, including the fuel filter, banjo filter (top of the fuel pump), throttle position sensor, and turbo pipework leaks. All these can fool the gearbox into conflict.

Thanks for the comments, all.
@alacrity - I realise that now having looked at the ratios in the manual, however the situation remains the same.

Update from the last few days. From cold start, shifts up fine, including torque converter lockup, but within seconds of that last shift TCC will drop out. Pretty much around the time the temp gauge gets to normal.
Stop and restart (with nary a pause), and she's fine for the duration.

I'd like to suggest it's a temperature sensor somewhere, I haven't checked the codes (literally just got back from Devon), or the P1521 code (although the solenoids do click).

It's a puzzle why it's just at that one specific time - it doesn't seem to matter if I let her warm up at idle either.