I experienced this code on a 7HBW23 Toyota pallet jack, but this can apply to other Toyota’s and Raymond electric pallet jacks. The error code C28 simply means the unit did not pass the self-test when first powered on. There is a list of possible causes (see below). Remember, when we are looking at self-test or startup failures, we must look at the obvious things first. A dead man pedal or tiller handle not in the rest position is very common on startup codes along with the main power switch not turned on. After you get past the obvious, look for the common causes like a blown fuse or a loose or broken wire.
List of Possible Causes
1. Main ON/OFF switch activate.
2. Low voltage to power amplifier (especially while lifting or driving)
possibly due to over-current or short-circuit. Try driving using
known-good battery.
3. PTC R1 missing, faulty, or tripped (very high resistance, due to
excessive current while main contactor is open; should automatically
recover). Carefully check to see if R1 is hot (tripped). If so, unplug
battery and allow it to cool. Locate low impedance path that tripped R1
and correct.
4. Wire #24 at 0V.
a. Check J5 not connected, fuse and wiring.
b. Check for 24V at J5-16.
5. Short or open circuit in CAN wiring, or electrical noise in CAN wiring
due to bad connection or outside interference, both at power ON.
a. Check CAN wiring.
b. Try operating truck in different environment.
6. Faulty power amplifier.
a. Check power amplifier for error code.
b. Check power wiring.
7. Lift contactor stuck closed
The main points and operation of this circuit
The unit will power up even with the main power switch in the off position, the error C28 will appear right away and is corrected when turning the main power switch on. If the code does not clear, check for battery positive to the main power switch. If there is no reading, check for battery positive to the R1 resistor just below the main power switch. There should be battery power on both terminals. CAUTION: Be careful grabbing this resistor as it may be hot and tripped. This is a power resistor that supplies the initial power to the controller so it can do the self-test.
If there is power on both sides of the resistor, there should be a pulsing light on the main controller. If there is no light on the controller, check the fuses located to the right side near the bottom of the controller. The power runs from the main switch to the R1 resistor and then to the downstream side of the main contactor. Then powers a fuse near the controller and then powers the controller to enable the self-test.
If the R1 resistor is hot, it is likely tripped and one of the wires at that resistor is batter negative. HINT: If the forks are all the way up and the unit is setting the C28 code, check continuity across the lift contactor, it is likely stuck closed. Tapping on the contactor lightly will sometimes free it up and the unit will begin to operate normally once the R1 resistor cools off and closes.
Summary
The common problems I have seen for this code is the pump contactor stuck closed.
The main power switch open circuit.
Blown fuse near the controller
J5 connector not plugged in at the controller