Gearbox jumped from R to 1&2

GazH32

Junior Member
Messages
38
Hi

On my way home yesterday (60 mile freeflowing A&B roads, doing normal speeds with no significant stop/starting) I stopped off and had to do a three point turn and then park up. While I was maneuvering and reversing the car it jumped from R to 1. At first I thought I must have knocked the paddles but then when I had parked up I had to wriggle the car back a bit and every time I selected R and applied power the car jumped to 1st and even 2nd on one occasion. The road was ever so slightly up hill but I wouldn't call it a hill or even much of a slope.

Anyway I left the car, picked up what I needed to pick up which took about 15 minutes and drove home. Once safely back on my drive I tested reverse a few times and all was good. This morning the car was fine for the school run and I tested reversing up a a slight incline and it all worked fine. I've just scanned the car and the only fault codes relating to the gearbox were P1770 - Gear engagements with wrong shifts and P1772 - Opposite gear engagement.

2011 4.7 MC, 67K miles, clutch is 11K miles @ 38% wear (as of last month), major service 6000 miles ago, no clutch slippage when driving, no oil on driveway.

If its not just a random Maserati glitch then I have a feeling its hydraulic oil quantity, condition or temperature related. If it was one of the F1 system valves then wouldn't the failure be more consistent? Has anyone else experienced this and found the cause?

Cheers

Gaz
 

Zep

Moderator
Messages
9,802
For it to go to a wrong gear it needs pressure to the right part of the actuator. If the TCU is shifting it (which it is) then it’s not a hydraulic oil issue. It’s a control issue.
 

GazH32

Junior Member
Messages
38
For it to go to a wrong gear it needs pressure to the right part of the actuator. If the TCU is shifting it (which it is) then it’s not a hydraulic oil issue. It’s a control issue.
Ok cheers. I take it then that hydraulic pressure is removed from the actuator once the gear is selected?

Are the any situations where it’s programmed to shift like this, such as a failsafe if it detects the car rolling forward?
 

spkennyuk

Member
Messages
6,146
Ok cheers. I take it then that hydraulic pressure is removed from the actuator once the gear is selected?

Are the any situations where it’s programmed to shift like this, such as a failsafe if it detects the car rolling forward?

Were you reversing up a very slight incline at the time ? Doesnt have to be much just enough of a slope that the car would roll slightly without your foot on the brake.

The TCU will behave as you have described if you select reverse while on a nose down facing hill. It will allow you to select reverse but if it senses the car roll forward it will eject reverse gear selection and go to 1st.

When this occurs it isnt a fault. It is the system getting its pants in a twist because the car is moving forwards and needs to be at a complete stop to engage reverse.

The error codes you would get for this scenario are P1770 and P1772.

Clear the codes and see if it happens again. I suspect it won't. If it does then you likely have a fault starting to manifest in the either the vertical or lateral sensor or an abs / wheel hub.

Basically if your on a very slight incline the hill hold does not kick in so the car can roll very slightly forwards after you select reverse. Car TCU says your going forwards you selected the wrong gear here is 1st gear.

If and abs sensor / wheel hub goes faulty then hill hold is disabled so the same can occur on any incline. You can avoid it in those circumstances by using the handbrake until the clutch has engaged. You would normally get a message on the display of Abs, traction control and hill hold unavailable if that scenario occured however i have seen cars that are not showing those errors but the abs/hub was faulty.

In theory if the vertical sensor and lateral sensor both think your moving forward when your not then the TCU would reject the reverse gear selection. Its highly unlikely that they are both going faulty at the same time.

The same error can occur for example if your on the flat coasting slowly to a stop in neutral but select reverse before you have come to a 100 % complete stop. Lateral sensor would tell the tcu that your going forwards so you cant have reverse gear.

The TCU will intervene for safety reasons / avoid damage to the gearbox in the following circumstances :

1. Wrong gear for direction of travel.
2. Revs too high for the gear selected.
3. Speed too high for the gear selected
4. Speed too low for the gear selected

There are others so not a complete list.

1st one is what i believe happened to your car.

2. If your doing 4k revs in 3rd gear and change down to second the TCU will allow it. If your doing 7.5k revs in 3rd and try to change down then the TCU could reject the request to avoid over revving the engine.

3. If your doing 130 mph in 6th gear and try to drop to 1st gear it would drop to 5th possibly 4th and then stop any further down shift until your speed is reduced.

4. You may well have seen in action already. If your stationary for example and accidentaly pull the paddle twice when selecting first gear the TCU will select first may briefly select 2nd and then drop back to 1st. The same would occur if you tried to select 6th gear from a standstill.

Appologies for the long explaination if you didnt need the additional info.
 

GazH32

Junior Member
Messages
38
Thank you @spkennyuk for the explanation, that's helped a lot.

The first time it happened during the 3 point turn I had thought that maybe the car had rolled forward but the second time when I was parking up I'm sure the car had started to move backwards and that I 'kept my foot in' to stop it rolling forward and it still jumped to first.

I'm going to keep an eye on it and next week I'll be able to pretty much recreate the whole journey and I'll try to be a bit more scientific.

I had a hub changed a few weeks back and know the havoc they can cause but there's no codes associated with another one yet. Where are the vertical and lateral sensors located? They're not under the passenger side footwell next to the ECU are they?
 

GazH32

Junior Member
Messages
38
First thing I would do is a gearbox relearn. Pop round mate
Cheers, I probably will pop round for a relearn but just for consistency I'm going to run it for a week to see if it comes back without changing anything else.

I have a couple of work trips to do next week and I'll run for about 60-80 miles on A roads and motorways and then pull in to some services and try reverse to try to recreate what happened before. That way with a car cleared of codes and no other changes since last time I might be able to get some useful information should it come back.

All was good this morning again on the school run though.
 

philw696

Member
Messages
28,179
Second that Matt.
Put a multimeter on and see what voltage you have and importantly what she drops to when cranking as that's when faults will get triggered.
 

conaero

Forum Owner
Messages
35,461
Just to remind you, once running, battery charging should be circa 13.7 dropping to 13.4 when warm up cycle completes.
 

GazH32

Junior Member
Messages
38
Ok, cheers for the figures, I’ll check it out and let you know what I find but she’s generally been pretty good in the mornings. The problem happened after a 2 hour drive in the afternoon.
 

Zep

Moderator
Messages
9,802
Do you keep your car on a battery conditioner? If your alternator reaching retirement age it is conceivable that it is giving you low voltage after a long run. Worth checking.
 

GazH32

Junior Member
Messages
38
No it’s not on a conditioner as it’s driven daily. I will check out the alternator though - I’ll throw the multimeter in the boot and check it whenever I stop.
 

GazH32

Junior Member
Messages
38
So on my way up the A34 this morning I stopped off and took some readings after about an hour and got 13.85V across the battery at idle with no accessories on. It was lower than I have tested other alternators to be which have normally been over 14 (but that's normally just after starting) and I did forget to put more load on and was unable to increase the rpm.

I stopped a second time and got 13.8V at idle (no accessories) and when I got to my hotel it was just over 13.8V (again no accessories).

When I stopped the second time something odd did happen though. I put the car in N and manually applied the EPB while I jumped out to check the clearance of my number plate to the kerb. When I got back in a yellow EPB warning was on the dash (the red parking brake/brake warning light was still on) and the 'N' was slowly flashing. I shut the car down and when I returned all was well again.

Another thing which could all be related is that I have noticed recently when I have parked up the EPB has indicated it has applied but as I have taken my foot off the brake the car slightly rocks (like an automatic when put in park) and I think the car is being held on the gearbox. The hill hold still works though. Maybe it just needs adjusting. There are no unusual noises or anything else pointing towards a problem.

I'm going to keep on monitoring it and will get a cigarette lighter voltmeter, I know they're not the most accurate , just so I can get a feel for what's happening when I'm driving and parking up. I'll also get some more readings with load and higher rpm when I get home. The battery is about 18 months old according to the invoices.
 
Last edited:

cakebread1

New Member
Messages
24
I had this. was a P1772 fault showing. Changed the gearbox oil and filter. Did a relearn on gearbox. yet still did it. Had to go to Maserati for them to plug in as only they have the full software package to solve it. Which they did. So the good news is it's not mechanical.
 

cheburator

Member
Messages
197
Happened to me once as I was parking the car in a small car park on the Northern side of the Stelvio this Summer. New clutch, with about 4k miles on it. Reset the errors using my ThinkDiag/Launch. Not had the problem since... Have done another 4k miles of mixed driving around Europe and the UK...
 

GazH32

Junior Member
Messages
38
I had this. was a P1772 fault showing. Changed the gearbox oil and filter. Did a relearn on gearbox. yet still did it. Had to go to Maserati for them to plug in as only they have the full software package to solve it. Which they did. So the good news is it's not mechanical.
Hi

Thanks for the reassurance but did they tell you what it was?

I have done about 800 miles since it last happened and I thought I had got away with it but I've just driven to Coventry (150 miles-ish), stopped a few times and all was good but as I got to the hotel car park I had to stop and get out for a ticket. I put it in N and applied the EPB, got out to get my ticket, got back in and selected first on the paddles and straight away an engine fault popped up on the dashboard. Went to park up and as I backed into a space (downhill this time) it jumped again from R to 1.

Switched it off and restarted it but the engine light was still on so I used my Thinkdiag tool and it brought up the same codes as before:

P1770 - Gear engagement with wrong shifts
P1772 - Opposite gear engagement

but this time an engine code came up too-

P0700 - Fatiesta Accensione Mil from gearbox ECU - Whatever that is!

A quick search and the only real hit was on this forum from 2013 when a similar issue was reported with suggestions of battery and oil/filter change but no real answers.

I cleared the codes and and did a quick bit of shuffling forwards and backwards and everything was fine.

@conaero - Any chance I can take you up on the gearbox relearn later this week or next week?

Cheers everyone for your suggestions.

Gaz
 

conaero

Forum Owner
Messages
35,461
Hi

Thanks for the reassurance but did they tell you what it was?

I have done about 800 miles since it last happened and I thought I had got away with it but I've just driven to Coventry (150 miles-ish), stopped a few times and all was good but as I got to the hotel car park I had to stop and get out for a ticket. I put it in N and applied the EPB, got out to get my ticket, got back in and selected first on the paddles and straight away an engine fault popped up on the dashboard. Went to park up and as I backed into a space (downhill this time) it jumped again from R to 1.

Switched it off and restarted it but the engine light was still on so I used my Thinkdiag tool and it brought up the same codes as before:

P1770 - Gear engagement with wrong shifts
P1772 - Opposite gear engagement

but this time an engine code came up too-

P0700 - Fatiesta Accensione Mil from gearbox ECU - Whatever that is!

A quick search and the only real hit was on this forum from 2013 when a similar issue was reported with suggestions of battery and oil/filter change but no real answers.

I cleared the codes and and did a quick bit of shuffling forwards and backwards and everything was fine.

@conaero - Any chance I can take you up on the gearbox relearn later this week or next week?

Cheers everyone for your suggestions.

Gaz
Yep I’m about, end of the week works for me