This code is very common, we often see it brought up multiple times per day across various Facebook groups. Diagnosis is as follows.

PO216 = 6.5L OBDII Trouble Code

DTC 34 = OBDI Trouble Code

This code will trigger any time DESIRED TIMING and ACTUAL TIMING vary more than 5* from each other. Ideally, they should never more than <1 degree of each other during normal operation.

DESIRED TIMING = Commanded timing advance from the PCM & Tune

ACTUAL TIMING = Measured timing advance of the injection pump/optic sensor TDC reference vs the crankshaft sensor TDC reference

*These values can be read, live, with a proper OBD scan tool for your model year

• Incorrect injection pump timing offset. TDCO (Top Dead Center Offset)

  • If the pump is set too far one way or another, the stepper motor can't achieve the correct timing advance/retard swing that is commanded by the computer

  • The first step in troubleshooting these codes should be doing a re-learn on the TDCO to see if it's set correctly. Simply move the pump and set the timing correctly to resolve.

• Faulty Stepper Motor

  • These can be field serviced by the end user, on the vehicle

• Seized advance piston in the DS4 injection pump

  • Very common in vehicles that have sat for extended periods of time

  • Old, varnished fuel or water in fuel are the main causes

  • Requires injection pump replacement

• Engine wiring harness fault

  • There'd most likely be multiple trouble codes if it was bad enough, however