P1691 — Fuel Injection Pump Controller Calibration Error — 5.9 Cummins 24-Valve (VP44)
P1691 is a Chrysler-enhanced code for the 5.9L Cummins 24-valve VP44. It indicates the VP44 pump controller reports a calibration error, often after a pump…
What it means
P1691 is a manufacturer-enhanced code meaning the VP44 pump controller reports a calibration error. On the 5.9L 24-valve this points to the VP44’s controller, often after a pump replacement or controller fault.1
Most likely causes
- VP44 pump controller calibration mismatch or corruption after pump replacement / reprogramming — The controller’s internal calibration data does not match the ECM expectation, commonly after a pump swap or ECM flash. Confirm power and grounds, then have the pump and ECM programming checked.1
- VP44 pump-mounted controller internal fault — Heat or electrical stress can cause the pump-mounted controller to fail internally, which can present as a calibration error. Check lift-pump pressure, VP44 power and grounds, and ECM-to-pump wiring before condemning the pump.2
- Loss of communication or power/ground issues to the VP44 controller — Intermittent ECM-to-pump data or power/ground loss can trigger controller-related codes. Check the ECM-to-pump data wiring and connectors, VP44 power and grounds (including the ground at the pump), and battery condition.3
- Companion module DTC pointer — P1693 indicates a fault stored in a companion module; P1691 may be referenced via a companion code. Read codes from every module and diagnose the companion code P1693 is pointing to.4
How to diagnose
- Verify code presence and freeze frame; clear and retest to confirm repeatability.
- Inspect VP44 electrical connector for corrosion, bent pins, and secure lock; check harness for chafing near the pump and valve cover.
- Test VP44 power and ground circuits per service specs; measure supply voltage at the pump connector with key on and cranking, and verify clean ground continuity.
- Check lift-pump supply pressure at the VP44 inlet; low supply pressure is a classic VP44 killer and stresses the controller.
- Inspect ECM connectors and grounds; verify battery condition and charging voltage to rule out low-voltage controller faults.
- If a pump was recently replaced, confirm correct part number and that ECM programming/calibration matches the installed VP44 controller.
- Use a scan tool to read all modules; if P1693 is present, retrieve the companion code it references and diagnose that code first.
- If power/grounds and supply pressure are good and calibration is verified, the VP44 pump controller is suspect and pump replacement with proper programming is indicated.
Specs and test values
| Check | Normal reading | When to measure | Source |
|---|---|---|---|
| Lift pump pressure at key-on | At least 10 psi (10–12 psi on a stock pump) | Key on engine off, during the ~25-second prime | Diesel Power Products |
| Lift pump pressure under load | Below 5 psi is a red flag for the VP44 | Accelerating or towing, gauge on the feed line | Diesel Power Products |
Common mistake to avoid
Replacing the VP44 without testing the lift pump first. A weak lift pump starves the VP44 of the fuel it uses for cooling, so a new pump installed on a bad supply side can fail again quickly. Put a gauge on the feed line and check pressure at key-on and under load before buying the pump. Source: Diesel Power Products — checking lift pump pressure on a 24-valve Cummins.
Parts and tools you may need
- Digital multimeter
- Scan tool capable of Chrysler enhanced codes and module reads
- Fuel pressure gauge for lift-pump supply test
- Basic hand tools for connector and ground inspection
Tools you’ll need
- OBD-II scan tool — Read and clear P1691 and any companion P1693 code to identify the referenced module fault and verify repeatability after repairs.
- Digital multimeter — Measure VP44 supply voltage, ground continuity, and ECM power circuits to rule out low-voltage or wiring faults affecting the pump controller.
- Fuel pressure gauge — Check lift-pump supply pressure at the VP44 inlet to confirm adequate fuel delivery and avoid controller stress from low pressure.
- Inspection mirror and flashlight — Visually inspect the VP44 connector, harness chafing near the pump and valve cover, and ECM connectors for corrosion or damage.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| ECM/PCM software update | — | 0.5–1.5 hrs | Shop |
| Shop diagnosis | — | 1–2 hrs | Shop |
| Wiring or connector repair | $10–$100 | 1–4 hrs | DIY with tools and a manual |
| VP44 injection pump | $800–$1,600 | 3–5 hrs | Shop |
Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.
When to see a pro
If the truck is non-running, stalls, or shows additional codes such as P1688, P0251, P1690, or P1689, have a diesel technician test VP44 power/grounds, lift-pump pressure, and ECM communication before replacing the pump. High-pressure fuel system work requires specialized tools and safety precautions.
Check for recalls
Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.
Sources
Spotted an error, or something missing? Tell us
Run a 5.9 Cummins 24-Valve (VP44)? This goes straight to the editor — it is not published.