This code came up on an electric Toyota pallet jack and may be applicable to other models.
Code Definition
Power amplifier could not detect the presence of the lower valve coil
The basic translation for this definition is: the controller on the unit looks for resistance in the lowering valve coil and if that reading does not get back to the controller, the code is set.
The controller sends out a voltage and looks for a certain voltage to return from the coil. If the return signal is not detected and this code is set, my first instinct would be that the lowering valve is disconnected or it has a broken wire that is creating an open circuit.
However, the first rule on any electric unit is to test the battery voltage. If an electric unit does not have enough battery voltage, the controller will have trouble powering up and it will still try to run the tests on the external components.
If the controller is trying to send out voltage to test the components and the battery voltage is weak, it will most likely fail those tests and you will get false error codes.
Additional problems caused by low battery voltage is that when voltage gets low, the amps get higher. When this happens, components such as relays and contactors that carry the current will start to over heat and the contacts within the components will start to burn; causing them to stick.
On this particular unit, there is a relay near the controller. If that relay experiences the low voltage it is common to start sticking. So after testing the battery voltage and verifying that the battery is sufficiently charged, start checking relays and contactors to make sure they aren’t welded closed. Most likely if a main contactor is stuck closed, the unit would set a different code because it looks for that too.
The official list of possible causes
- The lowering valve is missing.
- Open or short circuit in the lowering valve or wiring.
- Main relay missing or stuck open.
- Main contactor open circuit (especially after it has closed.
- Communication error due to power amplifier handset. Unplug handset from power amplifier. Allow handset to completely boot before turning truck on.
- Faulty power amplifier. Check power amplifier for error code.
This specific case it was the relay K4 located below the amplifier (controller). The contacts were stuck. Most likely caused by the customer running the battery too low.
These relays have two sets of contacts, for a quick test you can swap the wires on the contactor to the other set of pins and the unit should start working.
Warning: Make sure you have some electrical knowledge before attempting this and be sure that someone else hasn’t already done this from a previous code.