P0549 -- Exhaust Gas Temperature Sensor Circuit High Input Bank 1

P0549 - Exhaust Gas Temperature Sensor Circuit High Input (Bank 1)

Overview and mapping

• Based on the Open Source Code Definitions provided, P0549 corresponds to a high-input condition on the Exhaust Gas Temperature (translated: high signal of exhaust gas temperature sensor, bank 1) in the open-source code definitions.
• For context, OBD-II uses a standardized set of powertrain codes that monitor various emissions-related parameters and will set a fault when the signal is outside expected ranges. Wikipedia describes DTCs and powertrain codes within the OBD-II framework, including how the system monitors parameters and can illuminate the MIL when issues are detected.

Symptoms

• Check Engine Light (MIL) ON with P0549 stored or pending
• The vehicle may exhibit reduced power or unusual engine behavior if the PCM adjusts engine/aftertreatment control based on the faulty EGT input
• Possible diagnostic trouble code freeze-frame data showing abnormal EGT sensor readings or related parameter spikes
• Depending on the vehicle and scan tool, live data may show the Bank 1 EGT sensor signal sitting at an abnormally high value, or a rapid fluctuation to an out-of-range reading

Note: The specific symptoms can vary by vehicle, and some drivers may not notice obvious symptoms beyond the MIL until a road test or emissions test is performed.

Probable Causes

• Faulty or failing Bank 1 EGT sensor (high-output condition or sensor that reads high) - ~40%
• Wiring harness damage or connector problems to Bank 1 EGT sensor (short to power, short to ground, corrosion, loose pins) - ~25%
• Short/irregularities in the EGT sensor heater circuit or power/ground routing (if the sensor has a heater; or general electrical fault causing a high input) - ~15%
• PCM/ECU fault or software issue (less common, but possible) - ~10%
• Actual high exhaust gas temperature due to engine/an aftertreatment condition (e.g., engine running abnormally rich/lean, misfire, or a genuine temp rise detected by EGT) - ~10%

These estimates come from general field experience with EGT-related codes and the understanding that P0549 is an EGT circuit issue rather than a completely different subsystem fault. If you have access to NHTSA complaint frequency data for this exact code, that would refine these numbers, but such data isn't provided in .

Diagnostic Approach

1) Verify the DTC and data context

• Use an appropriate scan tool to confirm P0549 is present and note any freeze-frame data, engine RPM, vehicle speed, and operating conditions at the time of the fault.
• Check for other codes that may point to related systems (EGR, fuel trim, misfire, or sensor circuits).

2) Visual inspection and basic circuit checks

• Inspect the Bank 1 EGT sensor and its wiring harness for obvious damage, fraying, heat shielding faults, oil/condensate contamination, or loose/corroded connectors.
• Check for signs of exhaust system leaks upstream or downstream of the sensor that could affect readings or wiring integrity.
• Inspect the sensor's electrical connector(s) for bent terminals, corrosion, or contaminated pins. Disconnect and re-seat if appropriate, ensuring a clean, dry connection.

3) Electrical tests on the Bank 1 EGT sensor circuit

• With the ignition OFF, perform a resistance/check across the EGT sensor terminals as specified in the vehicle service manual (or compare against a known-good value for similar sensors). For sensors with a heater circuit, check heater resistance if applicable.
• With the ignition ON and the engine off (key-on, if permissible on your platform), back-probe or carefully probe the sensor signal wire, ground, and supply to verify voltages or resistance align with the manual's expected ranges. Look for:
  • Abnormally high sensor signal voltage or resistance outside spec
  • No signal or inconsistent readings
  • Heater circuit continuity if present
• Check the source of supply and ground references for the sensor circuit to confirm solid ground and clean 12V (or the sensor's supply voltage) in a steady-state condition.
  Note: Follow safe EGT-sensor testing practices; some sensors operate in harsh exhaust environments and testing should be done with engine off or with appropriate PPE and procedures.

4) Live data verification

• See if the EGT Bank 1 sensor reading correlates with engine conditions. If the sensor reads excessively high relative to expected exhaust temperatures for that operating condition, that supports a real high input condition or sensor fault.
• Check for abnormal readings from related engine sensors (MAP/MAF, O2 sensors, and fuel trims) that could cause actual exhaust temperature changes or misinterpretations by the PCM.
• Review any recent wiring changes or repairs that could have affected shielding/ground integrity around the EGT sensor circuit.

5) Determine root cause path

• If the Bank 1 EGT sensor tests out-of-range or displays high input with no wiring faults, replace the Bank 1 EGT sensor and re-test.
• If wiring/connectors show damage or corrosion, repair/replace the harness and repair grounds as needed, then re-check.
• If the sensor and wiring test OK, but the PCM still reports high input, consider software/ECU recalibration or a PCM fault; verify with vehicle-specific service information and possibly reprogramming or calibration updates.
• If the EGT sensor or harness tests pass yet engine conditions could genuinely produce high EGT, investigate possible engine conditions (misfire, rich/lean conditions, exhaust restrictions) with appropriate tests.

6) Post-repair verification

• Clear codes and perform a controlled drive cycle to re-check for P0549. Confirm there are no new DTCs and that live data shows stable, normal EGT readings for Bank 1 under various operating conditions.
• If the code returns, revisit wiring, sensor replacement quality, and any related control parameters (EGR system, exhaust leaks, or aftertreatment controls) as indicated by your data.

Tools Needed

• OBD-II scan tool capable of live data for EGT sensors and the Bank 1 circuit
• Multimeter or oscilloscope for circuit and sensor resistance/voltage testing
• Vehicle service manual for Bank 1 EGT sensor specifications (signal ranges, heater resistance if applicable, and wiring color codes)
• PPE and safe-work practices when working near hot exhaust components; do not touch exhaust components when hot
• General safety reminder: disconnect the battery or follow proper on-vehicle testing procedures as required by your vehicle and tool capabilities

Repair Options

• Replace Bank 1 EGT sensor if the sensor itself is confirmed defective
• Repair or replace damaged wiring or connectors to the Bank 1 EGT sensor
• Repair exhaust leaks or other exhaust-system-related issues that could influence EGT readings or sensor signaling
• If a software or ECU fault is suspected, consult vehicle-specific service information for appropriate calibration updates or reprogramming
• After any repair, perform a full drive cycle and re-scan to ensure P0549 does not return

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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