Follow this Real Fix to see how to diagnose P0105 and P0400 codes related to the MAP/BP and EGR systems on this 1999 Mercedes-Benz C280.
Vehicle
1999 Mercedes-Benz C280 2.8
Title
0105, P0400, Replaced Exhaust Gas Recirculation Valve, Manifold Absolute Pressure Sensor
Complaint
The customer states the check engine light is on.
Cause
Connected a scan tool and found codes: P0105 – Manifold Absolute Pressure/Barometric Pressure Circuit and P0400 – Exhaust Gas Recirculation “A” Flow. Used the scan tool to monitor live data and found the manifold absolute pressure (MAP) sensor specified 1.25 to 1.55 Volts at idle signal parameter was below specifications. Connected a lab scope to the MAP sensor, snapped the throttle while observing the voltage and waveform. The specified 1.25 to 3.8 Volt range was erratic and the waveform had dropouts. Performed a visual inspection of the MAP sensor and found no obvious faults. Disconnected the connector for the MAP sensor, inspected the connector, terminals and wiring harness and found no faults. Key on, used a multi-meter to measure the specified 5 Volt supply and less than 100mv ground at the MAP sensor connector and found both were present. Replaced the MAP sensor and continued diagnostics. Engine running, used the scan tool, commanded the exhaust gas recirculation (EGR) valve on and found the engine RPM should have dropped but did not drop. Used the multi-meter, backprobed the connector for the EGR valve to measure the specified 12 Volts supply and less than 100mv ground with the EGR commanded on with the scan tool and found voltage and ground were present. Disconnected the connector for the EGR valve, inspected the connector, terminals and wiring harness and found no faults. Used the multi-meter to measure the specified 25 to 30 Ohms resistance of the EGR valve solenoid and found no continuity. These test results verified the MAP sensor and the EGR valve were faulty.
Correction
Replaced the exhaust gas recirculation valve and manifold absolute pressure sensor, cleared codes, performed a road test and verified the vehicle operated properly. The check engine light did not illuminate and no fault codes returned.
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