Thread: '99 Grand Prix GT has code 1810, yet runs great as always, so why the code?

I had a little experience with this code when I rebuilt my tranny. The code is saying that the TFP switches are not giving the correct combination of highs and lows (voltage there or not there) for the individual gears that the shift selector is in. For example, if you are in the "D" position, a unique combination of the TFP switches are made. If these switches don't match up to the internal program in the PCM, then it flags the P1810 code. All of the wires from the TFP are passing throught the 20-pin connector located on the top of the tranny. If you have a scanner to look at this data, it's a simple matter of looking at the truth table (the combination of the high's and low's) as you go through each gear. This info is located in the service manual for the car or in the ATSG manual.

If you don't have a scanner, you'll have to use a voltmeter and backstab through the 20-pin connector to get access to these combinations through each gear. You'll have to be sure of course that you do have the +12V and ground for the switch. I'm at work now, so I don't have the diagram and truth table in front of me.

In my case, I rebuilt the tranny and even bought a new TFP switch. I even checked it out on the bench before I installed it. Everything looked good! After I cranked the engine, the check engine light came on. I got the P1810 code even with my careful preparation in checking it. Through a TechII scanner I own, I had an invalid combination of switches in Drive. After checking the wiring and finding nothing was wrong there, I knew something was wrong with the switch. So, I dropped the tranny down to remove the side cover and took the switch out. From the wiring diagrams, I knew the switch position and saw that the O-ring around the membrane switch was compressed. Of course, when you torque the TFP down, the o-rings will compress, but in this case, it actually made a NO switch a NC switch which would never release.

In the end, I bought a new switch, torqued it down and before I bolted the side cover on, I checked all the switches to be sure the combination was correct. That took care of the problem.

Sorry for the long post, but I feel that the more information one has, the better suited he/she can tackle a problem and get it solved.

Terry

Can you tell me which connector it is? There are two connectors next to the shift mechanism under the brake booster, and there is a round connector under the throttlebody at the highest point on the transmission. The two connectors next to the shift mechanism seem to small to have 20 pins, and the round one I can't seem to get it unplugged. I disconnected the PCM and reconnected it for now, in case that may help.

Let me know please, and thank you in advance for the help.

Originally Posted by McFly1999

Can you tell me which connector it is? There are two connectors next to the shift mechanism under the brake booster, and there is a round connector under the throttlebody at the highest point on the transmission. The two connectors next to the shift mechanism seem to small to have 20 pins, and the round one I can't seem to get it unplugged. I disconnected the ECU and reconnected it for now, in case that may help.

Let me know please, and thank you in advance for the help.

It will be the round connector located directly on top of the transmission which is probably about 1-1/4" in diameter. To release the connector, squeeze on the sides of the connector and then pull back while the connector is squeezed. As far as a scanner, a typical scanner will probably not be able to read this data of the switches. So, if you do get one, be sure it will be able to. Some of the guys in here use a tuner to modify the internal data of the tranny which of course shows you the tranny data. I'm sure it would be cheaper than a high end scanner. They could comment on this.

If the price of a scanner or software is too expensive, you'll need to use a voltmeteter/ohmeter to do your checking. I would keep the connector plugged up on the tranny with the engine running and just backstab through the pins so that you can analyze the switch combinations under actual conditions as you move the gear selector through each position. Otherwise, you'll throw more codes if you unplug the connector and there won't be any voltages at all going into the tranny. Or a better alternative would be to backstab the pins at the PCM which would check the entire wiring and you may find it a little easier to get access to the pins. Once you confirm that the switch or wiring is bad, you can unplug the connector (at transmission or PCM) and then use your ohmeter. I would have the engine turned off when you unplug the connector to do your checking. If you need a diagram or better yet a service manual of your vehicle, you can get one at www.alldatadiy.com In the manual, you'll see the pinouts of the connector, the truth table for the switches and all other pertinent information for your diagnosis.

Terry