P1800 Trouble Code; Symptoms, Causes, and How to Fix

The P1810 Transmission code means that the transmission is operating at full line pressure do to a problem TFP manual valve position switch or the wiring associated with it.  This switch opens and closes five different pressure switches, which control the transmission line pressure, and in turn has a direct impact on how hard your transmission is shifting.  It also has a transmission temperature sensor built into it.

P1800 Code Description


Symptoms of a P1800 Code

Causes of a P1800 Code

How to fix a P1800 Code

What transmissions can it affect?

P1810 Symptoms

Whenever the P1810 trouble code has been thrown, the transmissions line pressure is at it’s maximum.  That means that all shifts are going to feel incredibly harsh.  While it’s not the worst thing in the world for the transmission to run at max line pressure, it still causes it to wear and tear faster than under normal conditions.

Remember, the P1810 will turn the service engine soon light on.


P1810 Code Cause

The P1810 Code is usually caused by one of three things.

  1. The TFP Valve Position Switch will have a short circuit.
  2. The TFP Valve Position Switch will have a poor electrical connection.
  3. The Manifold Pressure Switch has gone bad.

Most of the time, it’s going to be that the Manifold Pressure Switch has gone bad.  The MPS lets the transmission know what gear that it is in.  Without this switch, it’ll operate at maximum line pressure all the time.  At maximum pressure, you’ll get incredibly hard shifts.

When diagnosing this code, always give the wiring harness a really good look before taking the pan off of the transmission.  There are situations where the culprit often is the wiring.  You don’t want to go through all the trouble of taking everything apart only to find out that it was a simple wiring issue.

The 4L80E is notorious for getting crud in it where the harness plugs into the transmission.  Or, the Chevy Cobalt is know for harness shorts right by the radiator on the drivers side.  It pays to take a look before turning any bolts.

Related:  4L60E Manifold Pressure Switch



P1810 Code Fix

Most of the time, the fix for the P1810 transmission code is going to involve dropping the pan and replacing the manifold pressure switch.  It’s a relatively easy fix most of the time.  It’s not buried or anything.

On a 4L60E or 4L80E all you’ll need to do is pop off the transmission filter and the manifold pressure switch will be right there.

Although it’s usually less likely that it’ll be a wiring harness issue, we recommend giving it a visual inspection before removing so much as a bolt from the transmission pan.  It only takes a few minutes to assess if there is any damage to the wiring harness.

What you are going to be looking for is a harness that has visible damage to it.  The best place to look is anywhere the harness touches metal or sharp objects on a car.  You would think that when these cars were designed, the engineers would avoid placing the wiring anywhere it could get damaged.  Apparently that’s not always the case.


Transmissions That Can Be Affected by the P1800 Code

The following is a list of transmissions that can be affected by this code.  If there are any that are left out, please feel free to comment below and I’ll update the article.  Really, it can affect all gm automatic transmissions that are computer controlled.

  • 4L60E
  • 4L65E
  • 4L70E
  • 4L80E
  • 4T45E
  • 4L85E