OBD-II Code P0548 — What It Means & How to Fix It

What Does This Error Mean?

P0548 means the PCM detected an abnormally low voltage signal from exhaust gas temperature sensor 2 on bank 1. This downstream EGT sensor monitors exhaust temperature after the diesel particulate filter or catalytic converter. A low voltage reading usually points to a short to ground in the circuit, a failed sensor, or a corroded connector. This code can interfere with DPF regeneration and exhaust after-treatment system monitoring.

Affected Models

2007 and newer diesel pickup trucks with DPF and EGT monitoring — Ford, GM, Ram diesel models
European diesel SUVs and sedans — BMW, Mercedes-Benz, Audi, Volkswagen diesel variants
Light commercial diesel vehicles with exhaust after-treatment systems
Turbocharged gasoline vehicles with dual exhaust temperature monitoring
Vehicles with SCR and DEF injection systems requiring precise downstream temperature data

Common Causes

EGT sensor 2 has shorted internally — the sensor element is shorted and sends a low or zero voltage signal
Signal wire from sensor 2 is shorted to ground — heat-damaged insulation caused contact with exhaust tubing or chassis ground
Moisture inside the sensor connector caused a short between the signal pin and ground pin
Corroded sensor threads have created an unintended ground path through the sensor body
PCM input circuit fault causing the sensor 2 voltage to be read as artificially low

How to Fix It

Connect a scan tool and check the live EGT bank 1 sensor 2 reading. With the engine cold, the sensor should read near ambient temperature. A reading at or below -40°F or showing 0 volts on a cold engine indicates a short to ground or complete sensor failure.

Also check for any related DPF or SCR fault codes that may have been triggered by the loss of sensor 2 data.
Raise the vehicle and locate EGT sensor 2 on bank 1 — typically found in the exhaust pipe downstream of the DPF. Inspect the sensor connector and wiring harness for visible signs of damage, especially heat damage near the DPF housing.

DPF housings get extremely hot during regeneration — temperatures above 1000°F are normal. Any wiring too close to the DPF body will eventually degrade.
Disconnect the sensor connector and check for moisture or corrosion inside the connector. Clean with electrical contact cleaner if needed. Check for continuity between the signal pin and ground with the sensor disconnected — any continuity indicates a harness short.

If moisture is the issue, seal the connector with dielectric grease after cleaning to prevent recurrence.
Measure resistance across the sensor element terminals. A good EGT sensor reads 100 to 300 ohms at room temperature. A near-zero reading confirms an internal short — the sensor must be replaced.

Even if the sensor tests acceptable on the bench, if the harness has a short to ground the code will return. Test both the sensor and the harness independently.
Replace the sensor if failed and repair any damaged wiring. Use high-temperature wire loom and heat shields to protect replacement wiring near the DPF. Clear the code and perform a test drive to confirm the repair.

On vehicles with active DPF regeneration, check that regeneration cycles complete normally after the repair.

When to Call a Professional

This sensor sits in a hot, inaccessible location under the vehicle near the DPF. If DIY diagnosis is beyond your comfort level, a diesel specialist can test and replace it in 1 to 2 hours. Typical repair cost is $200 to $500 depending on make, model, and sensor location.

Frequently Asked Questions

Can P0548 cause my truck to go into reduced power mode?

Yes — on diesel trucks, the PCM may limit engine output when EGT sensor data is missing or invalid. This is a protection measure to prevent exhaust system damage. Restoring a valid sensor signal usually clears the power restriction.

Is P0548 the same problem as P0545?

They are similar — both describe a low-voltage EGT circuit condition. P0545 refers to sensor 1 (upstream) and P0548 refers to sensor 2 (downstream). The cause and fix are similar, but the sensor location is different. Diagnose each sensor separately.

What happens to DPF regeneration when P0548 is active?

The PCM typically disables or limits active DPF regeneration when it cannot confirm downstream temperatures from sensor 2. This can cause the DPF to become progressively more clogged over time. You may notice a DPF warning light or reduced performance as the filter fills up.