Internal Fuel Injection Pump Controller Failure
Table of contents
P1688 DODGE Possible Causes
- Good Trip Counter Equals Zero
- Faulty Fuel Pump Control Module (FPCM)
- Fuel Pump Control Module (FPCM) harness is open or shorted
- Fuel Pump Control Module (FPCM) circuit poor electrical connection
How do I fix code P1688 DODGE?
Check the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector’s pins.
Tech Notes
- P1688 code is typically cause from low fuel pressure. Since the overflow valve is closed at 10 PSI that means there is no cooling fuel to keep the electronics cool so now they overheat and start to malifunction (P1688). Hence why I highly suggests the 14 PSI as a minimum instead of the FSM minimum of 10 PSI.
- Diagnosis And Testing
- A rubber tipped blow gun with regulated air line pressure is needed for this test.
- 1. Clean area around overflow valve and fuel return line at injection pump before removal.
- 2. Remove valve from pump and banjo fitting.
- 3. Discard old sealing gaskets.
- 4. Set regulated air pressure to approximately 97kPa (14–16 psi).
- 5. Using blow gun, apply pressure to overflow valve inlet end (end that goes into injection pump).
- 6. Internal check valve should release, and air should pass through valve at 97 kPa (14–16 psi). If not, replace valve.
- 7. Reduce regulated air pressure to 10 psi and observe valve. Valve should stay shut. If not, replace valve.
- 8. Install new sealing gaskets to valve.
- 9. Install valve through banjo fitting and into pump.
- 10. Tighten to 30 N·m (24 ft. lbs.) torque.
- Source: https://www.cumminsforum.com/forum/98-5-02-powertrain/450368-p1688-code-source.html#post4638821
Cost of diagnosing the P1688 DODGE code
The cost of diagnosing the P1688 DODGE code is 1.0 hour of labor. The auto repair labor rates vary by location, your vehicle’s make and model, and even your engine type. Most auto repairs shops charge between $75 and $150 per hour.
Possible Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
P1688 DODGE Description
Fuel Pump Control Module (FPCM) is monitored with ignition on engine off, and with the engine running. The P1688 code may set if FPCM, Powertrain Control Module (PCM) memory, programming or hardware error is detected.