Mode Selector Switch Signal V70 1998 Auto Tranny

Andrewoakland · Post by **Andrewoakland** » 25 Feb 2026, 11:00

Ok folks. Check Engine light came on so I broke down and bought a code reader. Fancy one too, iCarsoft specifically for older Volvos and Saabs. Plugged it in and it told me "Transmission control module fault: State NONE, MODE SELECTOR SWITH SIGNAL PERMANENT Faulty signal TOO LOW. It does not oddly, give me an actual P code
Also in addition to the check engine light, a big arrow shows up when ignition is in ON position before starting.
so is this my Neutral Safety Switch, PNP Switch or some other problem?

rrres · Post by **rrres** » 25 Feb 2026, 23:06

Mine is a '99, which had the flashing arrow and check engine light. When I scanned it, I got TCM-0039, which is "Gear shift position sensor Faulty signal". I figured might as well start by cleaning the PNP.

I found this thread...viewtopic.php?t=29930

I cleaned mine without disconnecting the harness. I also didn't remove the two shifter cable bracket bolts. The grease were hardened and gummed up the springs and copper contacts. After the cleaning and regreasing, so far the car is back to normal. I'm still monitoring it to see if something else shows up, but so far so good.

Start with the PNP and see if that solves it.

Andrewoakland · Post by **Andrewoakland** » 26 Feb 2026, 09:57

Very helpful Thanks

Louiseravot · Post by **Louiseravot** » 05 Mar 2026, 02:58

That message usually points toward the PNP switch or the mode selector switch on the transmission. On older Volvos those switches can get dirty or misaligned and send a “signal too low” fault to the transmission control module. I'd advise you check the connector and wiring near the gearbox because corrosion of the transmission module or a loose plug can cause the same issue.