OBD-II Diagnostic Trouble Code
P0198 — Engine Oil Temperature Sensor High
P0198 means the engine oil temperature sensor signal voltage is above the ECM's maximum. With a thermistor this reads as extremely cold oil. It usually means an open circuit, an unplugged connector or a signal wire shorted to voltage.
Severity 2/5
Truck-relevant
Service soon
Severity
Service soon
Engine Oil Temperature Sensor High
Code
P0198
Category
Powertrain
Subsystem
Cooling
Truck-relevant
Yes
What this means for truckers
P0198 (Engine Oil Temperature Sensor High) — sensor reading above plausible range. Verify with mechanical temp gauge before assuming sensor failure — if oil really IS overheating, you have a cooling problem.
Before you replace parts — try this first
P0198 on the Cooling system is most often unplugged or corroded connector — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Check-engine light is on, and oil temperature reads stuck at a very low value. Some diesels change cold-start, idle or fan strategies or use a default value. Drivability is usually normal.
Common causes
- CommonUnplugged or corroded connector ($50–$200)
- CommonOpen signal or ground wire ($100–$400)
- CommonOpen circuit inside the oil temperature sensor ($80–$350)
- RareSignal wire shorted to voltage ($100–$400)
How to fix
With a fused jumper, connect the signal terminal to the sensor ground terminal at the harness connector and watch for the reading to swing to the hot extreme.
When to use: First test
Check signal and ground continuity to the ECM.
When to use: When there is no swing
Replace the sensor.
When to use: When the wiring is good
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0100 — Mass or Volume Air Flow Circuit
- → P0101 — Mass or Volume Air Flow Circuit Range/Performance
- → P0102 — Mass or Volume Air Flow Circuit Low Input
- → P0103 — Mass or Volume Air Flow Circuit High Input
- → P0104 — Mass or Volume Air Flow Circuit Intermittent
Frequently Asked Questions
Can I drive with code P0198?
P0198 is severity 2 — service this week. Not an immediate stop, but ignoring it usually compounds the problem. Most common cause for this code is a worn sensor or minor performance fault that won't strand you today but will get more expensive the longer you wait.
How much does it cost to fix P0198 on a commercial truck?
Total repair cost ranges $50–$400 depending on the root cause. The cheapest fix is usually the first one listed below — Unplugged or corroded connector — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0198 fail a DOT inspection?
P0198 is generally not a direct DOT inspection fail item by itself. Inspectors focus on safety-critical systems (brakes, steering, tires, lights, hours-of-service). However, the check engine light alone can trigger additional inspection scrutiny. Best practice: fix the code and clear it before a planned inspection.
What's the difference between P0198 and related codes?
P0198 is closely related to: P0100 (Mass or Volume Air Flow Circuit), P0101 (Mass or Volume Air Flow Circuit Range/Performance), P0102 (Mass or Volume Air Flow Circuit Low Input), P0103 (Mass or Volume Air Flow Circuit High Input). These codes share the same subsystem (cooling) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0198 is set without the companions, the issue is more isolated.
How do I prevent P0198 from coming back after a repair?
For P0198 (Engine Oil Temperature Sensor High), prevention centers on the cooling system. Service cooling system at OEM interval. Use the correct coolant type — modern HD engines need ELC (Extended Life Coolant), not green/conventional. Pressure-test cap and system annually.