P0428Generic code

P0428 Code: Catalyst Temperature Sensor High (Bank 1)

The P0428 code means the signal from the bank 1 catalyst temperature sensor has gone above its maximum value. The main effect is reduced protection for the catalytic converter. An open circuit, a loose connector or a broken sensor ground 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

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What the P0428 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 P0428 code sets when that signal is too high, which usually means an open circuit, such as a loose connector or a cut wire, or an interrupted sensor ground.

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, measure the continuity of each wire between the component connector and the computer connector with the key off. It should be under 1 ohm, and an infinite reading means that wire is open. If the wiring is good, measure the component itself, because infinite resistance confirms it is open inside.

P0428 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 P0428 code

  1. Loose or broken connector. This is the most frequent cause.
  2. Signal or ground wire cut. The signal rises up to the reference.
  3. Sensor open inside, with infinite resistance.
  4. Short to 5 volts or 12 volts from rubbing against another wire.

How to diagnose the P0428 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 P0428 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.

P0428 on Nissan

Used on some older Nissan vehicles.

P0428 on Subaru

Used on some older Subaru vehicles.

P0428 on Toyota

Used on some older Toyota vehicles.

Frequently asked questions about P0428

Can I drive with a P0428 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 P0428?
Roughly $40 to $350, depending on whether it is wiring, a connector or the sensor. Diagnosing the P0428 code properly first keeps you from paying for parts you do not need.
What does the P0428 code mean?
It is a generic OBD2 code for a high input in the bank 1 catalyst temperature sensor circuit. The signal rose above its maximum value.
Will a P0428 code clear itself?
Only if the cause was a one-time glitch. An open wire or a failed sensor will bring the code back.

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