Fixing your PGM-Fi Main Relay.
Problems starting the car, usually after a short run
(when the interior is warm), though in bad cases the car
may fail to start at any time. A classic time for the
problem to occur is at the petrol station, or if you
park for a minute to get something from a shop. If the
car is parked for a long period, the interior usually
has cooled enough for the joint to make contact again,
and you won't notice a problem. As the cabin temperature
is a major feature of this problem, it might appear
worse on cold or rainy days when you have the heater
running to clear the windows etc. Extremely cold
temperatures can also cause the problem to be more
The engine will usually fire, run for a split second and
then stall, as the remaining fuel under pressure is used
When you turn the ignition key to position II (ignition
on) you should see the PGM-Fi indicator on the dash
light up and extinguish. Exactly timed with this lamp,
you should hear a click and the fuel pump turn on and
off. If you do not hear a click and the fuel pump, then
the main relay is likely to be at fault.
||A collection of main relays.
relay is used around 1985-1991, the small grey
type are used from 1992-1995 and the large grey
relay is used from 1995-2000+
The later 1995-on relays rarely go wrong, they use a
different design to the earlier version. Click here to
take a look inside.
The problem is caused by dry joints in the PGM-FI main relay. This relay controls power
to the ECU, and the fuel pump. Without power to the rest
of the fuel-injection system, or fuel pump, you won't be
Below is a diagram of the PGM-FI system fitted to
Honda's first fuel injected engine as fitted to the MK1
CRX. PGM-FI has
constantly evolved over the years but the function of
the relay is the same in
all Honda cars - to supply power to the fuel pump, and
On recent cars such as the
2001 Civic the current draw by the main relay is
monitored by the ECU, this way the ECU can tell if the
main relay is faulty.
Here are a few examples of what dry joints looks like. You can see the
fine crack in the solder between the pin and PCB track -
notice the others are OK.
Here we have a dry joint on
And another on relay #2.
|Notice that the other joints
are okay, it is always the two joints pictured
above that fail.
Dry joints are caused by vibration and changes in
temperature cracking the solder round a joint which has
not flowed correctly. They have a characteristic look,
and sometimes are very hard to spot, even to a trained
Remember it is not the actual relay itself that is at
fault, just the soldering. To repair the fault all we
need to do is remove the old solder and re-apply fresh.