P0428
Catalyst Temperature Sensor High (Bank 1, Sensor 1)P0428 is a generic OBD-II powertrain diagnostic trouble code: Catalyst Temperature Sensor High (Bank 1, Sensor 1). It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0428 means
P0428 — Catalyst Temperature Sensor Circuit High Input (Bank 1, Sensor 1) — is the electrical complement to P0427. The PCM has detected a signal voltage at the catalyst temperature sensor input that is above the maximum threshold for a valid reading. The indicated temperature is therefore impossibly high or pegged at the top of the measurement scale.
On NTC thermistor sensors, a high signal usually means an open circuit in the signal wire or within the sensor itself — because an NTC sensor's resistance rises sharply as temperature falls, a broken wire that leaves the input floating will read as maximum resistance, which the PCM interprets as an extremely cold temperature, but on many sensor supply configurations an open wire can cause the signal rail to pull high, depending on the PCM's internal pull-up arrangement. On thermocouple systems (common in diesel exhaust temperature chains), an open thermocouple lead or a broken reference junction produces an out-of-range millivoltage that the amplifier saturates high.
The practical consequences are the same as P0427 — complete loss of catalyst temperature feedback. On diesels with DPF this is a priority repair. On gasoline platforms the MIL illuminates and emissions monitoring is degraded, but immediate driveability impact is usually absent.
Common causes
Most-frequently reported root causes when P0428 is logged.
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1
Open circuit in the sensor signal wire between the sensor connector and the PCM.
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2
Internal open in the sensor element (broken NTC thermistor bead or broken thermocouple wire).
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3
Corroded or backed-out pin at the sensor connector leaving the signal rail floating.
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4
Open in the sensor ground or reference return wire causing the signal rail to be pulled high by PCM internal pull-up.
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5
Broken wiring harness due to heat damage or mechanical failure — more common near exhaust routing.
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6
Failed sensor from thermal overstress (e.g., from a prior runaway DPF regen).
Symptoms drivers notice
How to diagnose P0428
A typical diagnostic flow when this code is present.
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1
With KOEO, measure signal voltage at the sensor harness connector — a voltage at or near the PCM reference (5 V for NTC supply types) with the sensor disconnected is normal; if connected and still at maximum, the sensor element is likely open.
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2
Disconnect the sensor and measure resistance across sensor terminals — infinite (OL) resistance confirms an open sensor element.
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3
Inspect the wiring harness from sensor to PCM for breaks, burned sections, or pulled connectors.
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4
Check the sensor connector for backed-out or corroded pins by measuring continuity from connector to PCM pin.
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5
After confirming harness integrity, replace the sensor if internal open is confirmed.
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6
After repair, clear codes and verify with a live data check that the PID reads plausibly and tracks engine warm-up.
Related powertrain codes
- P0400 — Exhaust Gas Recirculation Flow Malfunction
- P0401 — Exhaust Gas Recirculation Flow Insufficient Detected
- P0402 — Exhaust Gas Recirculation Flow Excessive Detected
- P0403 — Exhaust Gas Recirculation Circuit Malfunction
- P0404 — Exhaust Gas Recirculation Circuit Range/Performance
- P0405 — Exhaust Gas Recirculation Sensor A Circuit Low
Frequently asked questions
Why does an open circuit read as "high" rather than "low"?
It depends on the PCM's internal circuit design. If the PCM has an internal pull-up resistor on the sensor input, a broken wire or open sensor leaves the input pulled to the reference rail, producing a high reading. If there is no pull-up, the input floats and may read erratically or at a default high value. Either way, the PCM recognises the value as outside the valid window and sets P0428.
Can a runaway DPF regen burn out the catalyst temperature sensor?
Yes. Uncontrolled or excessively hot DPF regens can expose the exhaust temperature sensor to temperatures beyond its rated range, burning out the thermocouple or NTC element and setting P0428. If you find P0428 alongside a history of DPF-related faults, inspect the sensor for physical heat damage.
Disabling P0428 in software
RaceTune can permanently disable P0428 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECUs with a P0428 disable in our catalogue
Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.
- Bosch EDC16C31 verified 1 software version
- Bosch EDC17C60 verified 1 software version
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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