Diesel Trouble Codes

P0197 — Engine Oil Temperature Sensor Circuit Low (7.3 Power Stroke)

Diagnostic reference for 7.3L Power Stroke 1999-2003 Super Duty/Excursion. HEUI injection uses engine oil pressure to fire injectors; there is no common rail…

Updated September 2, 2026

What it means

The PCM sees an abnormally low voltage/resistance from the Engine Oil Temperature sensor circuit. On the 7.3L Power Stroke the EOT sensor feeds injection-timing calculations. This is NOT a fuel-rail-pressure code; the 7.3L is HEUI and has no fuel rail or rail-pressure sensor.1

Most likely causes

  1. EOT sensor internal short / out-of-range low resistance — Sensor element failed low, pulling the signal toward ground. Typical electrical failure mode for a thermistor-type EOT.1
  2. EOT signal wire shorted to ground or chafed harness — Wiring from sensor to PCM is shorted to chassis/ground, or insulation chafed in engine harness, causing low voltage at PCM pin.1
  3. Connector corrosion / oil intrusion at EOT sensor — EOT sensor connector on the oil cooler/HPOP area gets oil-soaked/corroded, increasing leakage to ground and lowering signal voltage.1
  4. PCM reference-voltage or ground issue affecting EOT circuit — Shared 5 V reference or sensor ground problem makes the EOT reading read low; check PCM power/ground integrity before condemning sensor.1

How to diagnose

  1. Verify code and freeze-frame; confirm P0197 is present and not accompanied by other oil-pressure or ICP/IPR codes.
  2. Inspect EOT sensor connector and wiring for oil intrusion, corrosion, bent pins, and chafing along the engine harness to the PCM.
  3. Measure EOT sensor resistance at the sensor connector (engine cold vs warm) and compare to spec; a shorted sensor reads near zero ohms.
  4. Back-probe EOT signal wire at PCM connector; check for short to ground and verify 5 V reference and sensor ground integrity.
  5. Clear code, road test with live data; monitor EOT PID for plausible temperature rise with engine warm-up. If reading stays implausibly low, replace sensor and repair wiring as needed.

Parts and tools you may need

Rough cost and difficulty

Parts cost is modest; labor is driven by access to the EOT sensor on the oil cooler/HPOP area and harness inspection time.

When to see a pro

If wiring faults are found in the main engine harness or PCM connector, or if EOT readings remain implausible after sensor replacement, have a qualified diesel technician perform pin-out testing and PCM verification. Do not attempt high-pressure oil system disassembly for this code.

Sources

  1. Curated DTC seed — 7.3 Power Stroke (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎