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

Its a Trans Pressure Switch Malfunction code if you're referring to OBD 2 code P1810.

Change filter and fluid and check for extra metal or clutch stuff in the bottom of pan.

Clear code and see what the transmission does.

The code is for a pressure switch problem but many things can trip the code.
Speed sensors readings and bad wiring or lose connection or ground or 12 volt power lose to switch.
To check the code out.
You would need a engine/transmission scanner and a good volt/ohm meter to check out the wiring and switch and sensors.

Crusty stuff in dip stick tube is condensation and rust.
You need to lubercate your dip stick. :grinyes:
Just clean it as best as you can and smear a little greese on the dip stick and tube area.
Make sure a ac line or water leak is not above dip stick area.

I'd think it may be the pressure switch. Being electronic it can fail.

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

Fixed!

Here's my results. [Armed with a Digital Multimeter] I checked the ohm's resistance of the sensor, and it was off. Suppose to be no greater than 31ohms when at full temp, and instead it was 33ohms at about halfway to full temp.

That was a bit odd, but didn't prove much. I checked for continuity from the sensor harness to the PCM harness, and it was good. It's not possible to check continuity from the sensor to the PCM [without pulling the sensor from the tranny, and opening the PCM case], so I moved on.

Next, I checked for proper voltages when the shifter is in each position. I did it with the key on (but the engine off) at the PCM harness with the PCM disconnected, and I found certain voltages, but nothing changed [when I moved the shifter]. Then, I plugged in the PCM and backstabbed the harness [while checking w/the shifter in each position]... nothing changed again. I don't know how it's suppose to be done/how the sensor works exactly. Finally, I started the car, put the emergency brake, and did the backstabbing again [while checking w/the shifter in each position]... AHAH! That made a change.

Here's the pins I used:
Pin 22 Upper PCM Connector (it says the pin # right on the connector) - Signal A
Pin 57 Lower PCM Connector (it says the pin # right on the connector) - Signal B
Pin 17 Lower PCM Connector (it says the pin # right on the connector) - Signal C

Using those pins and stuzman's hand written truth table... I found that my Singal A was doing nothing what-so-ever. I backstabbed the connector on the sensor, and same thing. I then turned off the engine, but left the key on, and then checked Signal A while pluggin in and unplugging the connector. Lo and behold, there was voltage when I unplugged, but no voltage when I plugged in. This meant that the sensor was holding the voltage down to ground and then the voltage would come back when I didn't allow it to be connected.

Looking at the diagram of how the sensor works (it has a bunch of switches), it tells me that one of the switches is stuck closed/grounded. Next, I realized that if Signal A is left open, then by the truth table, the PCM thinks that you never went to Reverse or D1. Although, if Signal A is left to be grounded with what the sensor/switches are doing, the PCM sees an invalid combination of Signals, which results in a SES light. GREAT! I'll then just leave Singnal A disconnected, clear the code with a scanner, and see if the PCM complains [with a Service Engine Soon light].

SUCCESS! I disconnected Pin 22, pink wire, from the upper connector on the PCM (I just started carefully taking the connector apart until the pin was released)... taped it with some electrical tape, and then hid it within the harness connector back cover. Clear the code, and no more code.

No more Signal A... means:

Good News: no more code, no more Service Engine Soon Light... as the PCM thinks everything is fine, but PCM thinks that for some reason you never use Reverse and you never use D1. [This shouldn't hurt the transmission as the PCM merely assists by reving the engine for a smooth shift when it knows. I'll just take it easy if I need D1, reverse is a no brainer.]
Bad News: My Sensor is still bad and I will eventually replace it, but see Good News.

Originally Posted by McFly1999

Fixed!

Here's my results. [Armed with a Digital Multimeter] I checked the ohm's resistance of the sensor, and it was off. Suppose to be no greater than 31ohms when at full temp, and instead it was 33ohms at about halfway to full temp.

That was a bit odd, but didn't prove much. I checked for continuity from the sensor harness to the PCM harness, and it was good. It's not possible to check continuity from the sensor to the PCM [without pulling the sensor from the tranny, and opening the PCM case], so I moved on.

Next, I checked for proper voltages when the shifter is in each position. I did it with the key on (but the engine off) at the PCM harness with the PCM disconnected, and I found certain voltages, but nothing changed [when I moved the shifter]. Then, I plugged in the PCM and backstabbed the harness [while checking w/the shifter in each position]... nothing changed again. I don't know how it's suppose to be done/how the sensor works exactly. Finally, I started the car, put the emergency brake, and did the backstabbing again [while checking w/the shifter in each position]... AHAH! That made a change.

Here's the pins I used:
Pin 22 Upper PCM Connector (it says the pin # right on the connector) - Signal A
Pin 57 Lower PCM Connector (it says the pin # right on the connector) - Signal B
Pin 17 Lower PCM Connector (it says the pin # right on the connector) - Signal C

Using those pins and stuzman's hand written truth table... I found that my Singal A was doing nothing what-so-ever. I backstabbed the connector on the sensor, and same thing. I then turned off the engine, but left the key on, and then checked Signal A while pluggin in and unplugging the connector. Lo and behold, there was voltage when I unplugged, but no voltage when I plugged in. This meant that the sensor was holding the voltage down to ground and then the voltage would come back when I didn't allow it to be connected.

Looking at the diagram of how the sensor works (it has a bunch of switches), it tells me that one of the switches is stuck closed/grounded. Next, I realized that if Signal A is left open, then by the truth table, the PCM thinks that you never went to Reverse or D1. Although, if Signal A is left to be grounded with what the sensor/switches are doing, the PCM sees an invalid combination of Signals, which results in a SES light. GREAT! I'll then just leave Singnal A disconnected, clear the code with a scanner, and see if the PCM complains [with a Service Engine Soon light].

SUCCESS! I disconnected Pin 22, pink wire, from the upper connector on the PCM (I just started carefully taking the connector apart until the pin was released)... taped it with some electrical tape, and then hid it within the harness connector back cover. Clear the code, and no more code.

No more Signal A... means:

Good News: no more code, no more Service Engine Soon Light... as the PCM thinks everything is fine, but PCM thinks that for some reason you never use Reverse and you never use D1. [This shouldn't hurt the transmission as the PCM merely assists by reving the engine for a smooth shift when it knows. I'll just take it easy if I need D1, reverse is a no brainer.]
Bad News: My Sensor is still bad and I will eventually replace it, but see Good News.

Glad to hear that you found out that it was the switch assy. I figured it would probably be the culprit but was hoping for you that it would be a simple external fix such as a loose or broken wire. As you found out, you have to have the engine running to check the operation of the switches because each switch is located over a hole where the transmission fluid is directly applied to each switch membrance as it moves through the various gear selections. It's the pressure of the fluid that activates the switches. Anyway, you'll need to drop the tranny to gain access to the TFP switch assy. You can gain access to the switch assy by removing the side access cover. You won't have to separate the tranny from the engine, but it's still a little bit of a job. Once you get the cover off, the switch assy will be staring you right in the face and it's held on with five bolts. Congratulations on the troubleshooting, and I'm sure that others can benefit from your work.

Terry