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Error Code P1633 – Symptoms, Causes and Solutions

Life-sustaining memory (KAM) is used to store the various data of the driving cycle. It changes based on sensor inputs and driving. When the car battery is unplugged, the memory is erased and the PCM (Power Train Control Module) goes into standby mode. This controller uses the learned data for the correct operation of the motor.


The OBDII fault code P1633 on Ford, Mercury, and Lincoln vehicles indicates that the PCM has encountered a voltage lower than 10.5V in the Keep-Alive memory control circuit. This circuit delivers a constant voltage from the battery to keep the memory alive so the PCM maintains registration data.

Error code P1633 (Definition)

The error code P1633 means that the PCM (powertrain control module, also known as ECM or engine control module in other makes of vehicles) has detected a low voltage in the live memory circuit.

Read: P0203 OBD2 Error Code – Check Your Fuel Injector and Wiring!

This particular circuit supplies a constant voltage from the battery to keep the memory portion of the PCM alive so that it can continue to record data relating to the vehicle’s driving information such as fuel control, idle control, and strategies. adaptive transmission control, 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 should be checked for open or high resistance in the cable, short circuits, a blown fuse, and high voltage interference r/f of the ignition or charging system components. In rare cases, the PCM may be faulty as well, causing this error code.

Common symptoms

Like other error codes, this code activates the light Check engine and records the trouble code in the vehicle system.

Possible causes

This code is usually caused by an open live power circuit. (KAPWR) and a faulty PCM. However, the latter is rare.

How to check

To check this, you must first erase the codes with a scan tool. If the code is an on-demand issue (hard fault), it will not be cleared until the issue is repaired. If the code is a memory code, erasing the code with a scanner can easily get rid of the light Check Engine and prevent it from coming back, as long as 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 repair

To perform a repair, do the following:

Check the battery terminals; Inspect the cables and look for signs of corrosion and loose connections.

Note: If the KAPWR to the PCM is interrupted (occurs when the junction box is installed or the battery is disconnected), error code P0603/P1605 may be generated at first power-up.

If the battery terminals are in good condition, then do a Key Off, since the battery terminals are fine. Proceed to the next step. If there are problems or signs of damage to the terminals, then make the necessary repairs or replace the components that need to be replaced.

Next, check the engine compartment to see if the wiring is correct.

Check the EC system wiring (engine control) to see if it is close to the ignition components cables. If the wiring is too close to the ignition components or cables, then rearrange the wiring as necessary. If not, proceed to the next step.

Checks the power sustaining life (KAPWR) to the PCM.

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

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

While using a digital multimeter, hold the electronic EC harness and move, bend or shake a small section while working from the PCM to the instrument panel. If you get a voltage reading less than 10.5V, then it means you have an open circuit problem, which means you need to isolate and repair the open circuit.

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

Check to see if the error code repeats by reconnecting the PCM, starting the engine (slowly), and reaching the operating temperature. Then run the engine on/off self-test. It then retrieves the DTCs from continuous memory.

If the error code is present, then it means you need to replace the PCM. If the code does not appear after the procedure, then repair other error codes as necessary. If there are none, then the test is complete.

Remember that every time you disconnect the battery, the PCM will lose its power forget the learned information and settings, and return to factory program mode. This is why most vehicles take about 10 starts from cold to full operating temperature before the vehicle starts running like it did before the PCM lost its power.

If you want to know other articles similar to Error Code P1633: Life support supply voltage too low you can visit the category Fault Codes.


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