Ford code P1633

Keep alive memory P1633 on Ford

If you own a Ford Taurus or Mercury Sable and encounter a Ford code P1633 after repairing your air conditioning, read this first before spending a lot of time on diagnosis. The PCM requires constant power to retain learned settings. What is a learned setting? Well, the vehicle comes from the factory with set programming. As the engine ages, the computer is designed to alter the factory settings to account for worn rings, lower compression, worn spark plugs, etc. The PCM stores the modifying data in Keep Alive Memory. Any time you disconnect the battery or the PCM loses power, the PCM “forgets” the learned settings and reverts back to factory programming. That’s why it takes about 10 starts from cold to full operating temperature before the car starts to run like it did before the PCM lost power.

What does that have to do with your A/C?

Well, Ford, in it’s wisdom, powers the PCM with a 10A fuse #122. Unfortunately, that same fuse powers the A/C compressor clutch relay. When a compressor clutch burns out, it can draw excessive current, or it can just plain short out. That’ll burn up the 10A fuse.

You fix the compressor clutch, start the vehicle, feel the cold and then get a Ford code P1633. Well, dude, chances are you’ve got a blown fuse caused by the old compressor clutch coil.

Start by checking fuse #122. If it’s blown, replace it. Then clear the Ford code P1633 and restart. If the code resets, check the fuse again. If it’s blown, you’ve got a short between the battery junction box, A/C clutch relay, or the compressor clutch coil. Yank the relay and see if the fuse blows now. If it’s good, disconnect the connector to the compressor clutch. Reinstall the A/C clutch relay and check the fuse again. If it’s still good, the problem may be a short in the compressor clutch coil.

However, if the fuse doesn’t blow after replacing, disconnect the battery negative and then remove the connector to the PCM. Reconnect the battery and check for battery voltage at terminal 55 on the connector. If you don’t get battery voltage, wiggle the cables or backtrack until you find the open.

We can’t imagine what Ford was thinking when they wired KAM memory to the same fuse as the compressor clutch coil, but they did. And, since a bad clutch coil can often take out the #112 fuse, that’s why you see a Ford code P1633 after an A/C clutch repair

©, 2015 Rick Muscoplat