Diesel Trouble Codes

P0198 — Engine Oil Temperature Sensor Circuit High — 7.3 Power Stroke

P0198 on a 7.3L Power Stroke means the PCM sees the engine oil temperature sensor signal voltage above its valid range. On this HEUI engine the EOT sensor…

Updated October 15, 2026

What it means

Generic definition: The PCM sees the engine oil temperature (EOT) sensor signal voltage above its valid range. On the 7.3L the EOT sensor feeds injection timing and cold-start strategy. Circuit high is usually an open sensor, an unplugged or corroded connector, or an open signal/return wire; expect harder cold starts while the PCM runs on a default value.1

Most likely causes

  1. Open or high-resistance EOT sensor element — The sensor itself is open internally, pulling the signal toward reference voltage. This is the most common root cause for a circuit-high reading on the 7.3L EOT circuit.1
  2. Unplugged, corroded, or oil-contaminated EOT connector — The EOT sensor sits in the oil system; oil wicking into the connector or terminal corrosion raises resistance and drives the signal high.1
  3. Open or chafed signal/return wiring between sensor and PCM — A broken wire or chafed harness in the engine bay opens the circuit, causing the PCM to see high voltage on the EOT input.1
  4. PCM reference-voltage or ground issue affecting the EOT input — A poor PCM power/ground or internal reference problem can bias the EOT input high; this is less common but should be considered if wiring checks pass.1

How to diagnose

  1. Verify the code and freeze-frame conditions; confirm P0198 is present and note engine temperature at set.
  2. Visually inspect the EOT sensor and its connector for oil intrusion, corrosion, or loose terminals; clean and reseat as needed.
  3. Disconnect the EOT sensor and measure sensor resistance across its terminals at known temperature; compare to the temperature-resistance curve for the 7.3L EOT sensor. An open/infinite reading supports a failed sensor.
  4. With key on, engine off, back-probe the EOT harness connector: check reference voltage and ground at the harness side, then measure signal voltage to ground. Voltage stuck high with sensor disconnected points to a wiring/PCM issue.
  5. Perform a continuity and resistance check of the EOT signal and return wires from the sensor connector to the PCM connector; inspect for chafing, pinching, or oil contamination along the harness route.
  6. If wiring and sensor test good, monitor EOT PID with a scan tool while gently wiggling the harness and connector to reveal intermittent opens.
  7. Clear codes, road test with cold start, and confirm the EOT PID tracks plausibly with engine warm-up and that P0198 does not return.
  8. If the fault persists with a known-good sensor and verified wiring, evaluate PCM power/ground circuits and consider PCM input diagnostics per factory procedures.

Parts and tools you may need

Tools you’ll need

Rough cost and difficulty

Likely repairPartsShop laborWho usually does it
Wiring or connector repair$10–$1001–4 hrsDIY with tools and a manual
Temperature or pressure sensor (coolant, intake air, oil, fuel temp)$30–$1500.3–1.5 hrsEasy DIY
ECM/PCM replacement (programmed)$600–$2,0001–3 hrsShop

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 wiring tests pass but the code returns, or if you need PCM input testing, have a diesel technician perform pinpoint tests to avoid misdiagnosing a PCM issue. Do not attempt high-pressure oil system service for this code; P0198 is an electrical/sensor fault, not an HPOP/ICP issue. If cold-start performance is poor or you suspect related injection-timing effects, professional diagnosis is advised.

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 — 7.3 Power Stroke (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎