How to Read Trouble Codes From the ECU
On the gauge cluster, to the top left there are a few idiot lights which
are not on under normal driving conditions. One of these lights
reads 'check engine.' This light comes on when the ECU detects
a fault in one of the many electronic components from which it receives
signals and to which it transmits signals. If the ECU recognizes
a problem while the car is on, the 'check engine' light will be constantly
illuminated. If it has detected a problem in the past, but the
problem which it detected no longer exists, the light will be out.
However, the ECU will store a record of the faults it has detected in
the past until they are cleared deliberately or unintentionally.
To read any current or past faults, the 'check engine' light will flash
in a sort of Morse code, which we can decipher.
Underneath the steering column is a wide rectangular piece of plastic, the same color as the dash, which has a tray marked 'TRAY.' This large piece is held to the underside of the dash with a bunch of screws. Remove these screws and remove the plastic piece. Now there will be a bunch of wires for you to see. To the left of the steering column (at least in left hand drive cars) somewhere probably tucked away will be a bundle of wires with two pairs of electrical connectors which are disconnected. One is black and connects one wire to one wire, the other is green and roughly 'T' shaped, this one also connects one wire to one wire. With the car turned completely off, connect the black connector. Next, turn the ignition to 'ON' but do not start the car. The idiot lights in the dash will come on, and some may go out after a few moments. Watch the 'check engine' light and maybe have something you can write on to remember the codes. If there is a fault code in the ECU, the 'check engine' light will begin to flash in a particular manner. The codes range in number from 11 to 52, so we know that they all will be two digits. To signify the tens place of the number, the 'check engine' light will flash a long (1.2 seconds) flash. The single digit will be a short (.2 seconds) flash. Each flash within the same code will be separated by .3 seconds. Each error code will be separated by 1.8 seconds. Don't bother trying to time all these, just watch the light and you will begin to understand. Once the ECU has flashed all stored codes, it will loop through and repeat them. Now, for example, you see two long flashes followed by two short flashes. This means you have a code number 22. By looking at the following chart, we see that 22 is the code for the knock sensor. Once you have read and recorded all faults, turn the ignition off and disconnect the black connector.
If you have done the above procedure, you will likely wonder what the
green T-shaped connectors are for. These are for a more active
code reading procedure called D-check mode in the Subaru manuals.
Start with both connectors disconnected, start the engine, allow it
to warm up, then turn it off. Next, connect the test mode connectors
(green T-shape). Turn ignition to ON position without turning
on engine. At this point if the check engine light does not come
on, it is faulty and must be fixed before continuing. Depress
accelerator pedal to floor, return to half throttle and hold for two
seconds, then release. Start the engine. Now the light can
blink in two different ways. If everything checks out so far,
it will blink to indicate a number 01, 02, 03, 04, 05, 06, 07, or 08.
If a problem is already detected, it will blink according to the chart
below. Either way, your next step will be to drive the car with
the test mode connectors connected. You must drive over 7 mph
for at least one minute, and shift up to 4th gear if you have a manual
tranny. Now, either you will discover your trouble codes, or you
will have none.
Trouble Code Table