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low reference voltage fault code

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2010 FTC XLT Mini cargo w 158k.  the Chk engine came on w Mild hesitation.  Scanner reported MAP and Low Reference Voltage faults.  Replaced MAP and MAF sensors.  Wiggled those plus O2 connectors and wiring.  Cleared codes and then it ran ok for 25mi. Chk engine came back on w same codes.  Plus PCM fault too.  Any troubleshooting tips?  Thx

Edited by BobbyD

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The PCM sends a 5 volt reference signal to the engine sensors and then makes decisions based on the returning voltage. If the 5v signal is low, it will affect the returning voltage as well and can cause a variety of driveability issues. You will need a wiring diagram and a digital voltmeter. Start at the PCM and test for voltage coming out at the appropriate pin and connector. If the PCM is not putting out 5v you may have a PCM issue. Check power and ground to the PCM itself first before condemning the PCM. If it is 5v, you will need to follow the wiring diagram from the PCM through the different connectors until you find the voltage drop. Voltage drop per connection is max 0.1v. Any higher than that, you have a high resistance connection that will likely be the root cause of the codes and hesitation. Get some help if this is more than you're into. You want to make sure you don't cause any wiring harness damage during the diagnosis process. Good luck!

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