P0438Generic code

P0438 Code: Catalyst Temperature Sensor High (Bank 2)

The P0438 code means the signal from the bank 2 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 P0438 code means

This works the same as the bank 1 sensor, but on the converter on the side opposite cylinder 1. It only applies to V engines or flat (boxer) engines.

The sensor changes its resistance with temperature, and the computer measures the resulting voltage. The P0438 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.

Without the bank 2 signal, the computer cannot protect that converter and it turns on the check engine light. The most common fault is wiring burned by the heat of the exhaust.

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.

P0438 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 P0438 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 P0438 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. Compare it with the bank 1 sensor. With the engine cold, the two should match.

How to fix the P0438 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

  • 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 code is uncommon on current gasoline vehicles. Where it does appear, a loose connector or wiring broken by exhaust heat is the first thing to check.

Frequently asked questions about P0438

Can I drive with a P0438 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 P0438?
Roughly $40 to $350, depending on whether it is wiring, a connector or the sensor. Diagnosing the P0438 code properly first keeps you from paying for parts you do not need.
What does the P0438 code mean?
It is a generic OBD2 code for a high input in the bank 2 catalyst temperature sensor circuit. The signal rose above its maximum value.
Will a P0438 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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