P0427Generic code

P0427 Code: Catalyst Temperature Sensor Low (Bank 1)

The P0427 code means the signal from the bank 1 catalyst temperature sensor has dropped below its minimum value. The main effect is reduced protection for the catalytic converter. A signal wire shorted to ground or a missing 5 volt reference is the usual cause.

Severity
Low
Can I keep driving?
Yes, no immediate risk
Estimated cost
$40 to $350
Difficulty
Medium
System
Emissions Control
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

On this page

What the P0427 code means

Some vehicles measure the converter temperature with a dedicated sensor to protect it from overheating and, in certain markets, to turn on a hot converter warning. On diesels, similar sensors watch the temperature before and after the oxidation catalyst.

The sensor changes its resistance with temperature, and the computer measures the resulting voltage. The P0427 code sets when that signal is too low, which usually means the signal wire is shorted to ground or the reference is missing.

If the signal fails, the computer loses the converter protection. It normally turns on the check engine light and applies conservative strategies, for example enriching the mixture a little at full load to cool the exhaust. The sensor works at very high temperatures, and its wiring deteriorates with the heat.

To confirm it, unplug the component with the key on and watch what happens to the reading or the code. If the value jumps to the opposite extreme, the wiring is fine and the component is the one pulling the signal to ground. If nothing changes, look for the short in the wire, starting where the harness rubs against the engine, the chassis or the exhaust.

P0427 code symptoms

  • Check engine light on.
  • Reduced converter protection.
  • Incomplete emissions monitor, so the vehicle cannot pass inspection.
  • Often no other driving symptoms.

Likely causes of the P0427 code

  1. Signal wire shorted to ground by rubbing or heat.
  2. 5 volt reference shorted, if other sensors also fail.
  3. Damaged sensor with an internal short.
  4. Connector with water in it. This is very common on sensors mounted under the vehicle.

How to diagnose the P0427 code step by step

  1. Read the sensor value on the scan tool and compare it with what you expect.
  2. Inspect the connector for corrosion, water or loose pins.
  3. Check reference and ground, and measure the sensor resistance with the connector unplugged.
  4. Measure the signal with the connector plugged in and see whether it changes with conditions.
  5. Do a wiggle test on the harness while watching the reading.
  6. Check continuity all the way to the computer.
  7. With the engine cold, compare the reading with the ambient temperature.
  8. Measure the sensor resistance and compare it with the manufacturer table, since it varies a lot with temperature.

How to fix the P0427 code

  • Repair the connector or the wiring.
  • Replace the sensor if testing confirms it.
  • Correct the real condition if there is one, such as a leak or a blockage.
  • Clear the codes and complete a drive cycle so the monitor can run.

Technical reference data

  • High temperature sensor (thermistor or thermocouple).
  • Normal converter temperature: 400 to 800 °C (about 750 to 1,470 °F).
  • These are approximate values, so check the manufacturer data for your engine.

Brand-specific notes

This sensor is used on some older vehicles and on many modern diesels.

P0427 on Nissan

Used on some older Nissan vehicles.

P0427 on Subaru

Used on some older Subaru vehicles.

P0427 on Toyota

Used on some older Toyota vehicles.

Frequently asked questions about P0427

Can I drive with a P0427 code?
Yes. In general there is no immediate risk, and the problem is passing the emissions inspection.
Do I have to replace the sensor?
Only if testing confirms it. The connector and the wiring fail just as often as the sensor does.
Will I pass an inspection with this code?
No. The check engine light being on, or an incomplete monitor, keeps you from passing.
How much does it cost to fix P0427?
Roughly $40 to $350, depending on whether it is wiring, a connector or the sensor. Diagnosing the P0427 code properly first keeps you from paying for parts you do not need.
What does the P0427 code mean?
It is a generic OBD2 code for a low input in the bank 1 catalyst temperature sensor circuit. The signal fell below its minimum value.
Will a P0427 code clear itself?
Only if the cause was a one-time glitch. A shorted wire or a failed sensor will bring the code back.

Related codes

Questions about the P0427 code

There are no questions about this code yet. Tell us about your case: vehicle, symptoms and what you have already checked.