Diesel Trouble Codes

FC 1867 — EGR Temperature – Erratic, Intermittent or Incorrect (SPN 412 FMI 2) — Cummins ISX15

A diagnostic reference for Cummins ISX15 (2010–2017) FC 1867. Use it to identify why the ECM sees an erratic or implausible EGR temperature signal and to…

Updated October 15, 2026

What it means

The ECM is receiving an erratic or implausible EGR temperature signal from SPN 412. On Cummins ISX15 (2010–2017) this maps to FC 1867 and indicates the EGR temperature reading is erratic or implausible.1

Most likely causes

  1. EGR temperature sensor internal failure or drift — The sensor element is producing a noisy or out-of-range voltage, causing the ECM to flag the signal as erratic.1
  2. Wiring harness chafing or strain at the water jacket — The EGR temperature sensor harness is routed near the water jacket; heat and vibration can cause intermittent opens or shorts in the wiring.1
  3. Corroded or loose sensor connector / poor terminal contact — Moisture and heat degrade the connector, leading to intermittent signal loss or resistance changes.1
  4. ECM input circuit anomaly affecting SPN 412 — A rare ECM internal issue or reference voltage problem can make a good sensor appear erratic.1

How to diagnose

  1. Verify the fault is active and review freeze-frame data for engine speed, load and temperature at set.
  2. Inspect the EGR temperature sensor connector for corrosion, bent pins and secure lock; check harness routing near the water jacket for chafing, heat damage or strain.
  3. Perform a wiggle test on the sensor harness while monitoring live EGR temperature data to reveal intermittent opens.
  4. Compare live EGR temperature readings at idle and during a controlled load increase to a known-good baseline; erratic jumps suggest sensor or wiring.
  5. Check sensor supply voltage and ground at the connector against service specifications; unstable voltage points to wiring or ECM reference issues.
  6. If wiring and connector are sound, replace the EGR temperature sensor and re-evaluate the signal stability.
  7. Clear codes, run the engine through a representative drive cycle and confirm FC 1867 does not return.
  8. If the code persists after sensor and wiring checks, investigate ECM input diagnostics per Cummins service procedures.

Common mistake to avoid

Replacing the EGR valve without testing it. If the valve still moves freely, a carbon cleaning often fixes the flow code; and if it opens on command but the code stays, the blockage is in the passages or cooler, not the valve. Source: FleetRabbit — EGR valve problems and repair.

Parts and tools you may need

Tools you’ll need

Rough cost and difficulty

Likely repairPartsShop laborWho usually does it
ECM/PCM software update—0.5–1.5 hrsShop
Shop diagnosis—1–2 hrsShop
Wiring or connector repair$10–$1001–4 hrsDIY with tools and a manual
EGR position/temperature/differential pressure sensor$60–$3000.5–1.5 hrsDIY with tools and a manual

Typical US independent-shop figures; labor runs about $140–$200 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If the fault returns after sensor and harness service, or if ECM reference voltage is suspect, have a certified Cummins technician perform ECM input tests and harness integrity checks. Do not attempt high-pressure fuel system work. If the vehicle shows SCR derate or inducement codes, diagnose those companion faults first.

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

  1. Curated DTC seed — Cummins ISX15 (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎