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P1633 – What Does It Mean and How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


P1633 is an OBD-II Code that refers to Keep Alive Power Voltage Too Low


A P1633 code is a Ford manufacturer specific diagnostic trouble code that occurs when the PCM/ECM receives a signal indicating low voltage on the Keep Alive memory circuit. This circuit continuously maintains the battery voltage so that the PCM may continue recording information about the vehicle’s drive data, such as fuel control, idle control, and transmission control adaptive algorithms.

When the PCM detects a low voltage on the keep alive power circuit, it will set a P1633 code and illuminate the Check Engine Light.


Common causes for this code include:

  • Open or Damaged Keep Alive Power circuit
  • Bad PCM


The symptoms of a P1633 code are:

  • Illuminated Check Engine Light 
  • Normally no other symptoms


To diagnose a P1633 DTC code, a technician would:

  1. Scan for codes in the ECM and look at the freeze frame data for failure.
  2. Visually inspect the Keep Alive Power circuit for any damage or opens.
  3. Check the voltage on the Keep Alive Power circuit with a digital voltmeter.
  4. If all of the above tests appear normal, then the PCM would need to be replaced.

Common mistakes

The following are some of the most common mistakes that a technician may make when diagnosing a P1633 code:

  • Not thoroughly inspecting all the wiring and connectors.
  • Not checking the circuit voltage.
  • Not properly diagnosing the PCM as the cause of the code.

How serious is this?

A P1633 code is not a very serious code, but it can indicate that there is a problem with the Keep Alive Power circuit. If this circuit is not functioning properly, it can cause the battery voltage to drop, which may lead to further system problems.

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Repairing or replacing any damaged wiring or connectors.
  • Checking the voltage on the Keep Alive Power circuit and correcting any low readings.
  • Replacing the PCM if all other tests appear normal.

Related codes

A P1633 is related to and may be accompanied by the following codes:

P1630 – Keep Alive Memory Voltage Too High


In conclusion, the P1633 code is a diagnostic trouble code that refers to a problem with the Keep Alive Power circuit. This code may be caused by a variety of factors, such as a damaged circuit, a bad PCM, or low voltage on the circuit. There are a number of possible solutions that may fix this code, such as repairing or replacing any damaged wiring or connectors, checking the voltage on the circuit, or replacing the PCM.