What does it mean?
The troublecode P0100 is set when the MAF sensor circuit is malfunctioning. This code is similar to P0104 – MAF sensor circuit intermittent. The difference between the two codes is the consistency of the malfunction in the MAF sensor circuit. Troubleshooting will be the same for both codes. When diagnosing MAF sensor codes, understanding fuel trims is very important.
Please see the fuel trims article (P0171): Fuel Trims – Lean Identifying the type of MAF sensor in your car will also aid diagnosis. There are a number of different MAF sensors including the most common – hot-wire sensors. Note: “Circuit Malfunction” indicates that there is a malfunction in the control circuit, as opposed to a fault in a sensor or other component.
With “Circuit Malfunction” codes, replacement of sensors and components in the affected circuit will almost never resolve the problem, since as the code suggests, the trouble is in the circuit. This distinction between “circuit” and “sensor/component” is a great help to anyone trying to diagnose a circuit malfunction code, since it narrows the list of possible causes down considerably.
The causes of “Circuit Malfunction” codes are much the same as those for “Open Circuits” i.e., broken wiring, poor connections across electrical connectors or previously repaired wiring, loss of ground that prevents current flow, blown fuses, defective relays, faulty switches, or any of a host of other issues and problems that prevents a flow of current through wiring. Issues like high/low/intermittent voltages can set a “Circuit Malfunction” code on some applications.
Moreover, “Circuit Malfunction” codes could also indicate a problem with negative current control / flow, as well as issues with failed or failing PCM’s (Powertrain Control Modules), although control module failure is a rare event.