DTC Codes

Last update:

08/03/2005

Diagnostic Trouble Codes

Trouble Code Analysed

Readers of the On Board Diagnostics will know that the DTC consists of a single letter and four numbers. What they might not realise is that the code is not simply a sequential number from a list, but a code with its own meaning that relates to the concern to which it refers.

We will take the first OBDII code as an example, P0100 MAF circuit malfunction.

The DTC can be disassembled as follows:

Prefix	1st	2nd	3 & 4th
P	0	1	0 0

PREFIX:

Although the Vehicle Explorer software we use for the Ford Scorpio detects only the P codes at present, there are other OBD codes. These are:

	B - Body
	C - Chassis
	P - Powertrain
	U - Network

1st

The first number is not a zero value or a 1000 number - it is a code of 0 or 1.

	0 - If the code has the first numerical digit of 0 then the code is a generic - that is, standard, OBD code which will refer to every vehicle.
	1 - if the first digit is 1 then the code is described by the manufacturer and care must be taken to use the correct set of manufacturer PCM-specific OBD codes, or the results may be misleading. Our codes must be specific to the EECV powertrain control module (PCM)

2nd

The second number contains even more useful information - it shows what area of PCM operation the code refers to. These are

	1 - Fuel & Air Metering
	2 - Fuel & Air Metering - Injectors only
	3 - Ignition System or Misfire Monitor
	4 - Auxillary Emission Control System (Meaning EGR, Catalyst & EVAP systems)
	5 - Vehicle Speed Control and Engine Idle Control
	6 - Computer Output Circuits
	7 - Transmission
	9 - Transmission

3 & 4th

The last two numbers identifies the actual fault.

So by looking at the very first code P0100, before we even reach for a list we know that it is a Powertrain code which is OBD generic and that the code is related to the Fuel & Air Metering - which is exactly what the MAF does.