I started this thread about 2 months ago and thought I'd finish it for
anyone searching archives looking for solutions to their own P1810
problems. Plus I had a bit of a quandary with the VCM that never got
resolved this time around, which I hope could be addressed if anyone
has an opinion.
P1810 concerns the Automatic Transmission Fluid Pressure Manual Valve
Position Switch (TFP Val. Position Sw.) located in the transmission.
The TFP consists of five pressure switches (three NO, two NC). The
code P1810 sets when the VCM detects an invalid state of the TFP Val.
Position Sw. or the TFP Val. Position Sw. circuit by deciphering the
TFP Val. Position Sw. A service bulletin has been issued that the TFP
switches can get contaminated with metal or other junk from the
transmission fluid so that the TFP switches fails and P1810 sets. The
new TFP has a plastic cover to help prevent contamination of the
switches (note: mine had this plastic cover).
First I checked continuity of all wires and TFP contact to ground and
Then I removed the TFP unit and found a normally closed switch that
was intermittent. I cleaned up the switch (they are a simple design)
so that I was getting good conduction in the normally closed position
and an open circuit when the switch was depressed. All other switches
I never resolved a problem with the VCM. The Vehicle Control Module
(VCM) supplies the battery voltage for each of three range signals to
the TFP switch by way of the 20 pin connector on the transmission. By
grounding one or more of these circuits through various combinations
of the pressure switches, the VCM detects which manual valve position
you select. It seems simple enough; however, when checking my VCM
voltages to the TFP switch I noted that one of the three wires was not
giving 12 volts (rather <4V), so I went to a reputable auto recycler
and purchased a replacement VCM, but it had a similar low reading on
the same wire, so I replaced that VCM but had the same result. At
this point I didn't know what to think. The auto recyclers assured me
they were functional VCMs when removed from vehicles. The
intermittent TFP switch should not have shorted out the VCM, so I
assumed it was some kind of a mistake (perhaps I was overlooking
Hopeful that the switch I repaired on the TFP was the cause of P1810
and not the incorrect VCM voltage I was seeing, I put everything back
together (not a very hard job except for the messy transmission fluid)
and tried out the vehicle. P1810 set again within a few days. OK, I
didn't mind spending $20 to try a couple of used VCMs, but maybe that
just created more uncertainty. I decided to forgo $400 on a new
computer ($300 + $100 to flash ROM) and $60 on a new TFP switch until
I get a little more info, though I assume replacing both will solve
the problem (BTW not that I suspect this anymore, but the dealer
replaced/rebuit the transmission at one point in the vehicle's life).
For now I've obtained an E-check waver for the work I did on the
vehicle, but I will have to address the problem again in two years.