P0542 Subaru Hm Diagnostic Trouble Code

P0542 Subaru Hm code definition:
P0542 is a kind of OBD-II Diagnostic P-Powertrain Diagnostic Trouble Code for Subaru Hm.

P0542 Subaru Hm is a DTC or a diagnostic trouble code. It is a check engine light code which indicates that the catalyst's system efficiency is less than the required threshold. In simple terms, it means that more pollution is added into the air than what was supposed to be because of your car. There are two wires dedicated for each coil; one is battery feed which usually comes from the distribution center, and the other one for the coil driver circuit from the PCM. The PCM grounds or ungrounds the circuit to activate or deactivate the coil.

Symptoms

Symptoms of a P0542 Subaru Hm diagnostic trouble code may include:

The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.
Faulty PCM
If the DPF is not cleared the ECU will revert to the "Limp Home Mode" until the situation is corrected
Hesitation upon acceleration

Possible Causes :

A plugged converter will cause of host of driveability problems as well as set this code. A severely plugged converter will result in the inability to increase rpm when under load. Look for a code such as P0421 -- catalytic converter efficiency below threshold if the converter indicating a faulty converter.
Dirty air cleaner element Damaged DPF
An air leak forward of the DPF will change the sensor readings resulting in the code

Common Misdiagnoses

IC Circuit High Voltage Problem
Control Module Throttle Actuator Position Performance Problem
Air Conditioning (A/C) Clutch Feedback Circuit High Voltage Problem
Cruise Vehicle Speed/Set Speed Difference Too High Problem
PCM Stack Overrun Problem

Repair Processes :

Check to make sure they are not burnt or corroded. If in doubt, get some Electrical Contact cleaner at any parts store if cleaning of the terminals is needed. If the engine displays a miss and there wasn't a code, determine which cylinder is misfiring. If the exhaust manifold is visible, spay or pour a small amount of water on each cylinder exhaust port. Water will evaporate immediately on good cylinders and slowly on the missing cylinder. If this can't be accomplished pull the plugs and check the condition. Look for damage to the tank indicating impact that may have damaged the fuel pump or sender.

Process Tips

Diagnostic trouble code P0542 Subaru Hm is not difficult to diagnose and repair. Thus, it always pays to have a qualified technician to look after your vehicle should this error code arise.

Diagnosing this code requires the engine to be in good running shape, without unmetered air entering the engine. If other codes that relates to misfiring condition, lean running or air entering the engine is present, then you must first fix those error codes before P0542 Subaru Hm.

Fortunately, P0542 Subaru Hm is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.