Issues That May Arise With The H4A Automatic Transmission

Posted by on Wednesday, August 28th, 2013

The H4A is a four speed automatic transmission made by Honda. It is a modified version of the very first automatic overdrive transmission Honda ever made. It was first put into production in 1991 and remained so until 1997.  It was used in many popular Honda models, including the Accord and Vigor. The transmission is sometimes referred to as the following transmissions: PX4B, APX4, MPXA, MPWA, and MPOA.  While Honda generally makes very good vehicles and components there are some issues you may run into with this transmission. Let’s take a look at a couple of them.

The H4A automatic transmission can be found in the Honda Accord


The H4A is an electronic transmission, and an early design at that. This transmission is equipped with electrical solenoids that are used to control the shifting between gears. These early designed solenoids are nothing more that electrical / mechanical magnets. They consist of a coil of wire, that when energized, creates a strong magnetic field. The magnetic field causes a plunger inside the solenoid to move. This plunger is connected to a valve in the valve body, and when put into motion causes the transmission to shift gears. A built in spring returns the plunger to its original position once the current is disconnected from the solenoid.

It is within the coil of wire that most solenoid problems originate. The wire can either break (caused by excessive vibration) or can internally short out (caused by the wire getting too hot and the plastic coating around the individual strands of wire melting away).  It’s fairly easy to check the condition of a solenoid.

This is the H4A automatic transmission


First, hook an ohm meter to the two wires coming off the solenoid you want to test. If the solenoid is in good working order it should return a reading of somewhere between 20 – 30 ohms. Anything outside that range many indicate a problem with the solenoid. Second, check the spring inside the solenoid. You want to look for a broken or worn spring. Third, make sure the plunger is not stuck in its bore. Look for corrosion, a buildup of sludge or something interfering with the plunger, such as a chip of aluminum.

This is a solenoid from the H4A automatic transmission

You should also look for problems with the transmission wire harness. Given the age and mileage of many of these transmissions still in use, the wires harness can fail after many seasons from being exposed to the weather and road conditions. Look for wire harnesses that are worn through the protective outer plastic coating. Look for broken wires and corroded connections, too.

Sooner or later, due to high mileage or abuse, you will be faced with a decision to replace your A518 transmission. I highly recommend doing so with a re-manufactured transmission over one that was simply rebuilt. A re-manufactured transmission will include major internal modifications and upgrades designed to make it both stronger and more durable. A rebuilt transmission will not include this feature. A re-manufactured transmission also comes with a much better warranty; three years compared to an average 90 days for a rebuilt transmission. And in the rare event that you need to contact the company that re-manufactures transmissions, they are just a quick phone call or email away!

Leave a Reply

You must be logged in to post a comment.