Error Code P1633 is defined as Keep Alive Power Voltage Too Low.

This error code is a manufacturer-specific trouble code, meaning it does not apply to all vehicles makes. Rather, it applies only to specific vehicle makes, such as Ford. Specification on the definition, troubleshooting, and repairs still vary from one make and model to another.


Error Code P1633 means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has detected a low voltage on the Keep Alive memory circuit. This particular circuit supplies constant battery voltage to keep the alive memory part of the PCM so it can keep recording data regarding the vehicle’s drive information, such as fuel control, idle control and transmission control adaptive strategies, etc. If the battery is disconnected, or the voltage drops below 10.5V, the error code will be set.

If the battery has not been disconnected, then the circuit must be checked for open or high resistance in the wire, shorts, a blown fuse, high voltage r/f interference from ignition or charging system components. In rare cases, the PCM can be defective as well, causing this error code.

Common Symptoms

As with other error codes, this code activates the Check Engine light and registers the trouble code to the vehicle’s system.

Possible Causes

This code is usually caused by Open Alive Power (KAPWR) circuit and Faulty PCM. The latter is rare though.

How to Check

To check, the codes must first be cleared with a scan tool. If the code is an on-demand problem (hard fault), it will not clear until the problem is repaired. If the code is a memory code, clearing the code with a scanner can easily get rid of the Check Engine light and keep it from coming back, provided there is no fault present in the first place.

If the code is a hard code, then you will need a meter to access the PCM connector and check the voltages.

How to Fix

To conduct a repair, do the following:

Check the battery terminals; inspect the cables and looks for signs of corrosions and loose connections.

Note: If KAPWR is interrupted to the PCM (happens when the breakout box is installed or battery is disconnected), Error Code P0603/P1605 can be generated on the first power-up.

If the battery terminals are in good shape, then do a Key Off, as battery terminals are okay. Proceed to next step. If there are problems or signs of damage in the terminals, then conduct the necessary repairs or replace components that must be replaced.

Next, check the engine compartment for proper wire routing.

Check the EC (Engine Control) system wiring for proximity to ignition components of wires. If the wiring is too close to ignition components or wires, then reroute as necessary. If no, then proceed to next step.

Check the Keep Alive Power (KAPWR) to PCM.

Note: Refer to the PCM connector pin by the start of a pinpoint test. Do the pinpoint test by:

Disconnecting the PCM, measure voltage between the KEEPWR circuit at the PCM harness connector and ground.

While using a digital multimeter, hold the Electronic EC harness and wiggle, bend or shake a small section while working from the PCM to the dash panel. If you get a voltage reading that is less than 10.5V, then that means you have an open circuit problem, which means you should isolate and repair the open circuit.

If there are none, then that means nothing in the KAPWR harness circuit is deleted. For this, proceed to next step.

Check for a repeat of the error code by reconnecting the PCM, start the engine (slowly) and reach its operating temperature. Next, run Key On Engine Off Self-Test. Then, retrieve continuous memory DTCs.

If the error code is present, then that means you should be replacing the PCM. If the code doesn’t appear after the procedure, then repair other error codes as necessary. If there are none, then testing has been completed.

Remember that anytime you disconnect the battery, the PCM will lose its power and forgets the learned information and settings, and goes back to factory program mode. This is why it takes about 10 starts for most vehicles from cold to the fully operating temperature before the vehicle starts to run like when it did before the PCM lost is power.