Had a gearbox fault for the first time on my 4.4TDV8.
Last night I got onto the motorway and after a couple of miles it felt like the car shifted down a gear (constant speed, 70mph), then fault message came up and the car limped at 60mph.
Got off Mway, stopped engine (with a loud clunk when it stopped), restarted. Drove another 20 miles with no issues.

This morning, 2 mile drive to work, and it did something similar (but worse) - after stopping there was virtually no drive forward or reverse, but a metallic whirring sound. Repeated restarts didnt do anything.

I've read the codes:
P0721-62 (output shaft speed sensor - circuit range / performance - signal compare failure)
P0215-62 (vehicle speed/output shaft speed correlation - signal compare failure)

After reading the codes I had a play - after putting it into low range then back into high everything seems to be working normally.

Anyone recognise the fault?

Last edited by NDT on 13th Aug 2025 8:24pm. Edited 1 time in total

I assume you mean P0721 for the first code (typo?). The transmission output speed sensor is connected to the electronic module of the Mechatronic unit. I wonder if it might be worth disconnecting the 16-pin plug at the back of the transmission, checking the pins all look okay (not bent, corrosion-free) and then reconnect it again? Note that only 7 of the 16 pins are used with the 8HP70. Clearly this is a bit of a long shot.

Click image to enlarge

thanks Phil
The only code from the ABS was UO402-68 - invalid date received from TCM - Event Information.
I drove the car 2 miles home tonight and the problem didn't come back.

Having done a couple of flawless journeys, she’s failed again and I’m awaiting recovery on the hard shoulder.
How hard is a transmission swap?!

RRPhil wrote:

I assume you mean P0721 for the first code (typo?). The transmission output speed sensor is connected to the electronic module of the Mechatronic unit. I wonder if it might be worth disconnecting the 16-pin plug at the back of the transmission, checking the pins all look okay (not bent, corrosion-free) and then reconnect it again? Note that only 7 of the 16 pins are used with the 8HP70. Clearly this is a bit of a long shot.

RRPhil wrote:

Sometimes, output speed sensor codes are flagged because there’s a mechanical issue causing the output speed to not tally with what the TCM was expecting, and it incorrectly interprets this as a speed sensor fault. For example, when the spline on the transmission output shaft starts to fail due to fretting corrosion caused by lack of lubrication. Hopefully this is not the problem in your case.
Phil

Have you checked the front driveshafts? On mine the front right one sliped out and caused this metalic whirring sound and no drive. The first transmission guy changed the mechatronic, no change, the second transmission guy found the driveshaft sliping out every now and then. Meanwhile the transferbox was f**ked off so had to change that one too. About the same faultcodes as I recall.

Will check. First need to get it to do the fault again.

I changed a CV joint last month. Feels like that’s the obvious shaft to look at - although I was sure it was in properly.

Looks like it was the driveshaft. It’s been 4 weeks and 1500 miles since I reinstalled the driveshaft.
I didn’t fit a new snap ring on the diff end. Looks like it’s been slipping out - when jacked up yesterday I could pull it out of engagement easily.