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Scottdagoalie, Senior Master Tech.
Category: Ford
Satisfied Customers: 1940
Experience:  30 years with Ford dealers
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Code read P1633 what does this relate to

Resolved Question:

code read P1633 what does this relate to
Submitted: 6 years ago.
Category: Ford
Expert:  Scottdagoalie replied 6 years ago.



Thank you for asking your question on JustAnswer.



The code P1633 is caused by a loss of keep alive power source to the PCM (engine computer).This power source helps the PCM keep in memory the operations of the engine and transmission.If you had a low battery,disconnected PCM or had a lose connection in the power circuit,you can set this code.




DTCDescriptionPossible CausesDiagnostic Aides

P1633 - Keep Alive Power Voltage Too LowIndicates that the Keep Alive Power (KAPWR) circuit has experienced a power interrupt.
  • Open KAPWR circuit
  • Intermittent KAPWR
  • Damaged PCM
Loss of KAPWR to the PCM will result in a immediate MIL illumination and a DTC P1633.



QB: Diagnostic Trouble Code (DTC) P0603/P1633 QB: Introduction



    Note: If KAPWR is interrupted to the PCM (that is, when a breakout box is installed or the battery is disconnected), DTC P0603 can be generated on the first power-up.

  • Inspect the battery cables for loose connections, corrosion.

Are the battery terminal connections in good condition?

Yes No
KEY OFF. Battery terminals are OK. GO to QB2 . REPAIR battery terminals as necessary.


  • Inspect Electronic Engine Control (EC) System wiring for proximity to ignition components or wires.

Is wiring too close to ignition components or wires?

Yes No
REROUTE as necessary. Engine compartment wire routing is OK. GO to QB3 .


    Note: Refer to the PCM connector pin numbers in the beginning of this pinpoint test.

  • Disconnect PCM.
  • Measure voltage between KAPWR circuit at the PCM harness connector and ground.
  • While observing digital multimeter, grasp the Electronic EC harness and wiggle, shake or bend a small section while working from the PCM to the dash panel.

Does the voltage reading indicate less than 10.5 volts?

Yes No
ISOLATE and REPAIR open circuit. No open in KAPWR harness circuit detected. GO to QB4 .


  • Reconnect PCM.
  • Clear all DTCs that may have been caused by PCM disconnect.
  • Start engine and allow it to reach operating temperature.
  • Run Key On Engine Off Self-Test.
  • Retrieve Continuous Memory DTCs.

Is DTC P0603 or P1633 present?

Yes No
REPLACE PCM (refer to Section 2,Unable to duplicate or identify fault at this time. (Diagnostic Trouble Code (DTC) Descriptions for a list of possible causes.)


Customer: replied 6 years ago.
Alternator was replaced on friday drove vehicle for 2days why would the code have come up today after it had been running for more than an hour right after i engaged the 4wheel drive for a couple of minutes and then disengaged it and check engine soon comes on checked what code was being generated
Expert:  Scottdagoalie replied 6 years ago.
This may have been set during that repair and then set the light after a certain amount of time.The best way to check is to disconnect the battery for 3 minutes to reset the computer memory and see if the code returns.
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