Diesel Trouble Codes

P1693 — ... (5.9 Cummins 24-Valve (VP44))

P1693 is a companion/secondary code on the 5.9L Cummins 24-valve VP44 platform. It indicates the PCM has stored another fault in a separate module and is…

Updated September 2, 2026

What it means

P1693 means the PCM detected a fault code in another controller and is mirroring it. On this platform the code is a flag, not a primary engine fault. Retrieve companion codes from the PCM and the companion module (typically the transmission controller) to identify the actual failure.1

Most likely causes

  1. Companion fault stored in another module (e.g., transmission controller) – the actual DTC is in the companion module — P1693 is a flag that another module has set a fault. The root cause is the companion DTC, not the engine itself. Read codes from all modules and address the companion code first.1
  2. PCM communication / data-link issue preventing companion code retrieval — Intermittent CAN/PCI bus or power/ground issues can cause the PCM to set P1693 when it cannot read the companion module. Verify module communication, powers, grounds, and data-link integrity before assuming a hard fault.1
  3. Recent module replacement or reflash with mismatched calibration — After module service, a mismatch or incomplete flash can cause the PCM to mirror a spurious companion fault. Confirm module part numbers and calibrations match the 1998.5–2002 5.9L VP44 configuration.1

How to diagnose

  1. Verify platform applicability: 5.9L Cummins 24-valve VP44 1998.5–2002 with Bosch VP44 rotary pump, fixed-geometry HX35/HY35 turbo, APPS pedal, grid heater, no EGR/DPF/SCR/common rail.
  2. Use a scan tool to read all modules. Record the companion DTC(s) referenced by P1693; P1693 alone is not diagnostic.
  3. If no companion code is present, check PCM powers, grounds, and data-link connections for corrosion/loose terminals.
  4. Clear codes, cycle ignition, and re-scan to confirm P1693 returns with or without a companion fault.

Parts and tools you may need

Rough cost and difficulty

Cost varies with the actual companion fault. P1693 itself requires no parts; diagnosis is scan-tool time. Repair cost is driven by the underlying companion DTC.

When to see a pro

If companion codes indicate internal transmission faults, high-pressure fuel system work, or require module programming, have a qualified diesel technician perform diagnosis and repairs. Do not attempt safety-critical or high-pressure fuel repairs without proper training and equipment.

Sources

  1. Curated DTC seed — 5.9 Cummins 24-Valve (VP44) (curated) ↩︎ ↩︎ ↩︎ ↩︎