If you’re having shift issues on your Smart Fortwo, P0707 & P0914 error codes [The signals from the incremental sensor of component M17 (Gear motor) are implausible] that you just can’t clear and the transmission “teach-in” function keeps failing its well worth checking the transmission (gearbox) wiring loom where it passes close to the chassis.
Removing the left-hand rear wheel (passenger side in the UK) will help gain enough access to be able to look up just in front of the suspension coil and inspect the wiring loom, if you notice ANY damage to the cloth tape or can see any wires inside you will need to pull out the loom and inspect it.
To get access to the loom the “easiest” option (still a royal pain in the arse) is to unplug all the connectors from both the shifter motor and clutch actuator (there are a couple of zip ties you’ll also need to cut) then pull the loom through from the rear then out into the wheel arch.
You will then have enough slack to properly inspect the loom and perform any repairs if required.
TOP TIP: If the wires are broken they will no doubt be oxidised making them nearly impossible to solder but you can easily remove the oxidisation with some hydrochloric acid (brick acid works).
Good evening,
I have a 2008 Smart 451 which runs like a charm in all weathers, except moderate to heavy rain. In these wet conditions, the car will drive for some time, then the gear change becomes erratic and jerky, before ultimately the car stubbornly goes into neutral. Having just done a deep dive on Google, I came across your post. The damage you are describing is right by the wheel, so would be exposed to a lot of spray.
How complex is the procedure to remove the whole harness for testing and repair?
Many thanks for the great write-up! Stuart
The harness comes from the TCU under the passenger seat (assuming you’re in the UK) and it goes along the main chassis rail with a spur to the clutch actuator before finishing at the selector motors.
It’s clipped to the fins on the casting of the gearbox; the place to inspect is where it rubs against the chassis rail.
You have a few options if the loom is damaged:
1) Replace the whole thing.
2) Remove it and repair the broken wires with some heat shrink and some suitable wire to bridge the damage.
3) Repair in situ (very possible just a little fiddly)
The issue you’ll face if you repair is the copper will be corroded but this can be reversed with a strong acid with brick/concrete acid probably being the easiest to source.