P0548 - Exhaust Gas Temperature Sensor Circuit Low Bank 1 Sensor 1
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0548 indicates that the Engine Control Module (ECM) has detected a low voltage condition in the Exhaust Gas Temperature (EGT) sensor circuit for Bank 1, Sensor 1. This sensor is typically located before the catalytic converter or Diesel Particulate Filter (DPF). The ECM monitors the voltage drop across the sensor; a 'low' signal usually signifies a short circuit to ground in the wiring or an internal failure within the sensor itself. Since accurate EGT data is crucial for DPF regeneration and turbocharger protection, the ECM may limit engine power (Limp Mode) to prevent thermal damage.
Possible Causes
Short circuit to ground in the EGT sensor wiring
Failed Exhaust Gas Temperature sensor (internal short)
Corroded or damaged connector pins
Internal Engine Control Unit (ECU) fault
Symptoms
Recommended Solution
- Visual Inspection: Check wiring near the exhaust manifold for melting or chafing. Inspect the connector for oxidation.
- Voltage Test: Disconnect the sensor. With ignition ON, check for a 5V reference from the ECM. If 0V, verify wiring back to the ECM.
- Resistance Test: Measure the resistance across the sensor terminals. At 20°C (68°F), it should typically be between 200-500 Ohms. A value near 0 Ohms indicates an internal short.
- Scan Tool Live Data: Monitor the EGT Bank 1 Sensor 1 pid. If it shows a static, implausible value (e.g., 0°C), the circuit is faulty.
- Replacement: Replace the EGT sensor if internal resistance is out of spec. Clear codes and perform a test drive.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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