P0195 means the engine control module found the engine oil temperature (EOT) sensor circuit outside the range it expects. It is the general "circuit" code for that sensor; the more specific members of the family are P0196 (range or performance), P0197 (low), P0198 (high) and P0199 (intermittent). Some manufacturers use P0195 for any fault on the circuit, others use it only when the reading is implausible against other temperature sensors on a cold start. Read the definition on the scan tool for the vehicle: Chrysler calls it "Engine Oil Temp Sensor Input Circuit," Nissan and Honda call it a "signal circuit error."
Severity: low on most gasoline engines, moderate on diesels. Can you keep driving? Yes. On a gasoline engine the oil temperature reading is mostly a comfort and protection input: it may drive an oil temperature gauge, help decide when the oil life monitor counts a cycle, and on some engines delay high-rpm operation until the oil is warm. Losing it turns on the check engine light and not much else. On a Power Stroke diesel, oil temperature feeds injection timing, fuel quantity, glow plug operation and on the 6.0 L and 7.3 L the high-pressure oil system that fires the injectors, so a bad reading produces hard cold starts, rough running and poor power. Even there the engine runs; it just runs badly until the sensor is fixed.
Where the sensor is, and why that matters
The EOT sensor is a thermistor screwed into an oil passage where the oil is hot and moving. Locations that come up most:
- Ford Power Stroke diesels: on the 7.3 L it sits on the high-pressure oil pump reservoir at the front of the engine; on the 6.0 L it threads into the high-pressure oil pump cover under the turbocharger; on the 6.4 L and 6.7 L it is on the oil filter housing or cooler. All of these are hot, oily and hard to see, and the connector takes years of heat cycling.
- Ram 1500 with the 5.7 L HEMI (2014 to 2023): on the side of the oil filter housing near the alternator, easy to reach, with a connector that owners on the Ram forums report failing before the sensor does.
- Nissan Altima and Frontier: on the oil filter bracket or the block near the filter.
The reason location matters: this sensor sits where oil leaks land. A weeping filter housing gasket or oil cooler seal fills the connector with oil, and oil in a connector corrupts a thermistor signal long before it corrodes anything. Pull the connector and look before doing anything else.
How a two-wire thermistor is tested
The sensor has two wires: a 5-volt reference through a resistor inside the module, and a ground return. The thermistor's resistance falls as oil warms, so the voltage the module sees on the signal wire falls too. The module converts that voltage to a temperature and compares it against the coolant temperature and intake air temperature sensors. After a long cold soak all three should agree within a few degrees; if the oil reading is far off, or sits at the top or bottom of the range, the code sets.
That design gives three clean tests:
- Signal voltage with the sensor unplugged, key on: about 5 V. That proves the reference and the signal wire from the module.
- Signal voltage with a jumper across the two pins, key on: near 0 V. That proves the ground wire. If it stays high, the ground is open.
- Sensor resistance across its two pins at a known temperature, compared with the manufacturer's chart. A typical automotive thermistor reads a few thousand ohms cold and a few hundred ohms hot. Infinite means open, zero means shorted.
With those three numbers you know whether the fault is the reference, the signal wire, the ground or the sensor, and no part has been bought yet.
Causes, in the order they are found
A connector contaminated with oil or corroded. The most common cause on both the Ram HEMI and the Power Strokes. Oil wicks up the wires by capillary action, the terminals lose tension, and the signal drifts or drops out.
A damaged wire near the sensor. The EOT harness on a diesel often runs close to the turbocharger and the exhaust up-pipe, and insulation hardens and cracks. On the HEMI the wire near the alternator can rub the alternator bracket.
The sensor itself. Thermistors do drift with age, and a drifted sensor sets the range or performance version of the code (P0196) more often than P0195. A sensor that reads open or shorted at room temperature is a sensor.
A shared reference or ground problem. If several temperature sensors set codes together after a cold soak, the fault is the shared 5-volt reference or a shared ground, not three sensors at once. The reasoning is the same as for any circuit code.
The module. Last, and only after the three tests above have passed and the fault persists with a new sensor.
A diagnostic order that respects the two-wire design
- Record the code and its companions before clearing. Note whether coolant temperature or intake air temperature codes sit beside it. Pull the freeze frame: the oil temperature value recorded at the fault (often a default such as minus 40 or plus 250 °F) tells you whether the module saw an open or a short.
- Compare the three temperature readings after a cold soak. Key on, engine off, after the vehicle has sat overnight. Oil, coolant and intake air should all read close to ambient. An oil reading that is wildly different is the fault; a plausible reading means the fault is intermittent.
- Pull the connector and look. Oil inside, green corrosion, loose terminals, a seal that has hardened. Clean or repair before testing.
- Run the three tests: 5 V unplugged, near 0 V jumpered, sensor resistance against the chart. Flex the harness while watching the signal voltage to catch an intermittent.
- Fix what failed. A wire repair, a connector, or the sensor, in that order of likelihood. Do not replace the sensor because the code names it; replace it because it measured wrong.
- Clear and verify with a cold start the next morning, because the plausibility check that sets this code runs on a cold soak, then let the readiness monitors complete.
What P0195 does not tell you
It does not say the oil is hot, cold or low. It says the circuit that reports oil temperature gave the module a number it could not accept. It does not distinguish the sensor from its connector or its wiring, and on a Power Stroke it does not tell you that the hard starting you noticed is a symptom rather than a separate problem. The two-wire test does all of that in a few minutes.
Frequently asked questions
Can I drive with a P0195 code?
Yes. On a gasoline engine the oil temperature reading is a minor input and the engine runs normally with the check engine light on. On a Power Stroke diesel the module uses oil temperature for injection timing and glow plug control, so expect hard cold starts and rough running until it is fixed, but the engine is not at risk from the sensor fault itself.
Is the engine oil temperature sensor the same as the oil pressure sensor?
No. The oil pressure sensor or switch sets the P052x family (P0520 through P0523) and drives the oil pressure warning light. The oil temperature sensor is a separate thermistor and sets P0195 through P0199. On some engines they sit near each other on the oil filter housing, which is why they get confused.
Why did P0195 set after an oil filter housing or oil cooler leak repair?
Because oil from the leak got into the sensor connector, or because the harness was disturbed during the repair. Pull the connector, clean it, check the terminals for tension and run the two-wire test before replacing the sensor.
How much does it cost to fix P0195?
A connector cleaning or a wire repair is under an hour of labor. The sensor is an inexpensive part; on the Ram 5.7 L it is a few minutes to replace, on a Power Stroke it can take an hour or more because of where it sits. A module is the expensive outcome and comes last.
Related codes
- P0196: engine oil temperature sensor range or performance. The reading is plausible but wrong, usually a drifted sensor.
- P0197 / P0198: engine oil temperature sensor low or high. An open or a short, with the module reading a default value.
- P0199: engine oil temperature sensor intermittent. A connection that opens and closes.
- P0115 through P0118: engine coolant temperature sensor circuit, the sensor the module compares oil temperature against.
- P0520 through P0523: engine oil pressure sensor or switch, a different sensor on the same part of the engine.
The code number itself tells you the family and the domain; how to read an OBD2 code number explains what each character means.