An oil temperature sensor sends a lower voltage as the oil gets hotter. If the voltage drops so low that the reading looks hotter than oil could ever get, the engine computer knows the circuit has failed. A P0197 code means the engine oil temperature sensor signal voltage is too low.
This guide explains why low voltage means a hot reading, what causes it and how to test the circuit.
P0197 Code Breakdown
Every OBD-II code follows the same five-character pattern set by the SAE J2012 standard. Each character narrows down which system has the fault. This table shows what each part of the code tells you.
| Character | Meaning | What It Tells You |
|---|---|---|
| P | Powertrain | The fault is in the engine or transmission systems. |
| 0 | Generic (SAE) code | The definition is the same on every OBD-II vehicle. |
| 1 | Fuel and air metering | The fault involves the sensors that measure air and fuel. |
| 97 | Specific fault | Engine Oil Temperature Sensor Low |
What the P0197 Code Means
The SAE J2012 standard defines the P0197 code as Engine Oil Temperature Sensor Low. The sensor is a thermistor whose resistance falls as oil heats up. The powertrain control module (PCM) sends a 5-volt reference through it and reads the voltage that returns.
Hot oil means low resistance and low voltage. When the voltage drops close to 0 volts, the scan tool shows an impossibly hot oil temperature, often 300°F or more. The PCM then decides the circuit has failed low.
That usually means the signal wire is shorted to ground or the sensor has shorted inside. The PCM may run the cooling fans, limit engine speed or switch to a default value.
Signs of a Low Oil Temperature Sensor Signal
A false hot reading can trigger engine protection. Common signs of a P0197 code include:
- Check engine light on
- Oil temperature reading extremely hot on the scan tool or gauge
- Cooling fans running all the time
- Reduced power or limited RPM on some engines
- Oil temperature warning on the dash
What Causes the P0197 Code?
Low input faults almost always come from a short. These are the usual causes:
- Signal wire shorted to ground. Chafed insulation touching the block or pan pulls the voltage down.
- Internally shorted sensor. The thermistor fails with near-zero resistance.
- Oil inside the connector. Oil and dirt can bridge the pins.
- Damaged wiring near the oil pan. Road debris and heat wear through insulation.
- PCM fault. Rare.
How to Test the Circuit
You need a scan tool, a digital multimeter and the wiring diagram.
Confirm the Hot Reading
With the key on and the engine cold, compare oil temperature with coolant temperature. An oil reading far hotter than coolant on a cold engine confirms the low signal fault.
Do the Unplug Test
Unplug the sensor with the key on and watch the scan tool. The reading should drop to about -40°F, since an open circuit looks extremely cold. If it does, the wiring is fine, and the sensor is shorted inside. If it stays hot, the signal wire is shorted to ground.
Check for a Short
With the battery disconnected and the sensor unplugged, check for continuity between the signal wire and ground. Any continuity means a short. Inspect the wiring along the oil pan and near exhaust parts.
Repairs That Clear the P0197 Code
Fix the cause, then clear the code and confirm a normal reading in live data.
- Replace the oil temperature sensor if the reading drops to -40°F when unplugged.
- Repair a shorted signal wire and protect it with loom.
- Clean oil out of the connector with electrical contact cleaner.
- Replace a leaking sensor so oil stops reaching the connector.
A little oil may drain when you remove the sensor. Have a pan ready, use a new seal or thread sealant as required and check the oil level afterward.
Before you order parts, check the coolant temperature sensor reading as well. If both oil and coolant read impossibly hot at the same time, the shared 5-volt reference or sensor ground may be at fault rather than the oil sensor itself. Fixing that shared wire clears both readings at once.
Repair Cost Breakdown
Most P0197 code repairs cost little. This table shows typical ranges.
| Repair | DIY Cost | Typical Shop Cost |
|---|---|---|
| Wiring repair | $10 to $30 | $100 to $300 |
| Connector cleaning or pigtail | $10 to $40 | $75 to $200 |
| Oil temperature sensor | $20 to $80 | $100 to $250 |
Is It Safe to Drive with a P0197 Code?
You can usually drive carefully. Before you do, check the coolant gauge and oil level to rule out a real overheat.
If the reading is false, the PCM may limit power or keep the fans running, which drains the battery after shutdown on some vehicles. Fix the circuit soon.
Related Codes
These codes often show up with this one or point to the same system:
| Code | Meaning |
|---|---|
| P0194 | Fuel Rail Pressure Sensor Circuit Intermittent |
| P0195 | Engine Oil Temperature Sensor Malfunction |
| P0196 | Engine Oil Temperature Sensor Range/Performance |
| P0198 | Engine Oil Temperature Sensor High |
| P0199 | Engine Oil Temperature Sensor Intermittent |
Fixing a Low Oil Temperature Signal
A P0197 code means the oil temperature sensor voltage is too low, so the PCM sees impossibly hot oil. Shorted sensors and shorted wires cause most cases.
- Compare oil and coolant temperatures on a cold engine.
- Unplug the sensor and watch for -40°F.
- Check the signal wire for a short to ground.
- Replace the sensor if the wiring tests good.
Frequently Asked Questions
Is My Engine Actually Overheating?
Probably not, if the coolant gauge reads normal and the oil temperature reading looks impossibly high on a cold engine. Still, check the coolant gauge and oil level before driving. A real overheat shows up on the coolant gauge too.
Why Do the Cooling Fans Keep Running?
Many PCMs turn on the fans when they see high oil temperature. A false hot reading from a shorted circuit makes the fans run constantly, even on a cold engine. Fixing the sensor circuit stops the fans from running when they should not.
Can Oil in the Connector Cause the P0197 Code?
Yes. Oil that seeps past a worn sensor seal can travel up the wires into the connector. Oil and dirt together can create a path between the pins and lower the voltage. Clean the connector, and replace the sensor if its seal has failed.
Is the P0197 Code the Same as P0198?
No. They are opposites. The P0197 code means the voltage is too low, usually from a short. P0198 means the voltage is too high, usually from an open circuit. The unplug and jumper tests quickly show which one you have.
Where Should I Look for a Shorted Wire?
Start where the wiring runs close to metal edges, the oil pan, the exhaust and any brackets. Look for shiny spots where insulation has worn through. Check any spot where the wiring was moved during earlier repairs, since a pinched wire often shorts against the engine block.