P0437
Catalyst Temperature Sensor Circuit Low (Bank 2, Sensor 1)P0437 is a generic OBD-II powertrain diagnostic trouble code: Catalyst Temperature Sensor Circuit Low (Bank 2, 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 P0437 means
P0437 — Catalyst Temperature Sensor Circuit Low Input (Bank 2, Sensor 1) — is a hard electrical fault: the PCM has measured a signal voltage at the Bank 2 catalyst temperature sensor input that is at or below the minimum threshold for a valid reading. This is the Bank 2 mirror of P0427.
On NTC thermistor sensor designs the signal voltage tracks sensor resistance, which falls as temperature rises. A "circuit low" condition means the signal rail is being pulled toward ground — typically caused by a short to ground in the signal wire or a shorted sensor element whose resistance has collapsed to near zero. On thermocouple-based exhaust temperature sensors (common in diesel exhaust chains), an excessively low millivoltage output can indicate a short between the two thermocouple conductors, a reversed junction, or loss of the PCM amplifier reference. In either case the PCM reads an impossibly cold Bank 2 catalyst temperature — often pegged at or below ambient — and sets the fault.
The functional impact on gasoline platforms is primarily emissions-related: the MIL illuminates and catalyst monitoring is disabled for Bank 2. On diesel platforms where a Bank 2 temperature sensor is part of the DPF management circuit, loss of feedback can degrade regen quality. Repair priority should be elevated on diesel vehicles.
Common causes
Most-frequently reported root causes when P0437 is logged.
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1
Signal wire for the Bank 2 catalyst temperature sensor shorted to chassis ground between the sensor connector and the PCM.
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2
Internal short within the sensor element (NTC thermistor resistance collapsed to near zero, or shorted thermocouple junction).
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3
Water, coolant, or road-spray intrusion into the sensor connector creating a low-resistance path to ground.
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4
Chafed wiring harness where the signal conductor contacts the exhaust pipe, chassis, or engine block.
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5
Loss of PCM reference voltage to the sensor circuit, causing the signal line to be pulled toward ground by the sensor's internal resistance.
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6
Incorrect sensor fitted with an excessively low resistance characteristic that reads below the PCM minimum threshold at normal temperatures.
Symptoms drivers notice
How to diagnose P0437
A typical diagnostic flow when this code is present.
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1
Connect a scan tool and verify the Cat Temp B2S1 PID is reading at the low-pegged value; record all companion DTCs.
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2
With KOEO (key on, engine off), probe the signal wire at the sensor harness connector — a near-zero voltage with the sensor still connected indicates a short to ground in the wiring or within the sensor.
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3
Disconnect the sensor and re-measure signal wire voltage at the harness connector; if it rises to near the PCM reference voltage (typically 5 V for NTC supply circuits), the sensor element itself is shorted internally.
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4
With the sensor disconnected, measure resistance across the sensor terminals with a multimeter — near-zero ohms confirms an internal short; compare to the manufacturer specification.
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5
Trace the signal wire from the sensor connector to the PCM, inspecting for chafing points against the exhaust system, body panels, or heat shielding.
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6
Check the connector for moisture ingress, corrosion, or pushed-back pins.
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7
After confirming harness integrity, replace the sensor if the internal short is confirmed.
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
What does "circuit low" mean — is the catalyst actually cold?
No. "Circuit low" refers to the electrical signal being below the PCM's minimum valid voltage threshold, not to the physical temperature of the catalyst. It usually indicates a short to ground in the wiring or an internally shorted sensor element. The actual catalyst temperature is not measured when this fault is active.
Is P0437 the same fault as P0427 but for Bank 2?
Yes. P0437 is the Bank 2 counterpart of P0427. The electrical fault mechanism, diagnostic approach, and likely causes are identical; only the location of the sensor and wiring run differs.
Can moisture in the connector cause P0437?
Yes — water or road salt intrusion into the sensor connector creates a conductive path that shunts the signal wire toward ground, producing a false low reading. After repairing the short, clean the connector thoroughly, apply dielectric grease, and check the harness routing for any sources of water ingress.
Disabling P0437 in software
RaceTune can permanently disable P0437 — 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.
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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