P04D6 — Exhaust Brake Input Circuit High

Causes

• Open or damaged wiring in exhaust brake input circuit
• Connector corrosion, bent pins or poor mating at switch/ECM
• Exhaust brake switch or control module failed (stuck open or internally shorted)
• Short to battery voltage (charging circuit) on the input wire
• Faulty ECM input circuitry or intermittent internal fault
• Aftermarket equipment or recent repairs that affected wiring

Symptoms

• Malfunction Indicator Lamp (MIL) or fault light on
• Exhaust brake fails to engage or only works intermittently
• Driver may see a message or reduced functionality related to exhaust brake
• Noisy or abnormal exhaust brake behavior when commanded
• Related drivability or regen/exhaust control faults in some vehicles

What to check

• Read and record freeze frame and live data for exhaust brake input with a scan tool
• Verify code is current and not pending; clear and recheck if needed
• Perform a thorough visual inspection of wiring, connectors, and harness routing between switch and ECM
• Back-probe the exhaust brake input pin and measure voltage with key ON/engine OFF and while operating switch
• Check continuity to ECM and to ground; check for short to battery voltage
• Wiggle test wiring while monitoring input for intermittent changes

Signal parameters

• Typical input architectures use a pull-up to a reference (5 V or vehicle battery) or an internal pull-down to ground — expected idle states vary by design
• When switch is active: input often pulled to low (approx. 0–1 V) or to a defined logic voltage depending on design
• When switch is inactive/open: input may be near reference (approx. 5 V or battery voltage) — a reading significantly above the designed reference (e.g., >5.5 V on a 5 V system or >13.5 V on a 12 V referenced input) is considered high
• Expected DC resistance of a closed mechanical switch: near 0 Ω; open switch should be very high/OL
• Use manufacturer's wiring diagram/connector pinout to confirm expected levels and thresholds

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