How to test the power transistors

[luv2rallye]

To test the 2.0L power transistors:

This test will check the power transistors for go/no go operation. If it fails your transistors are bad. Note that the power transistors may still be weak, intermittent, or fail with temperature which this test does not check for (although you can sometimes make them fail when you heat them with a hair dryer or heat gun which I strongly recommend).

Background: This test is better than the one in the manuals (which use an ohmmeter) for the following reasons:
1) The manual version requires an analog ohmmeter which most people don’t have and can’t get easily anymore (and why buy one for just this test?). A digital one, which all people have in their multimeter, will not work.
2) The ohmmeter’s probes polarity must be correct (analog ohmmeters actually have their polarity reversed which the manual version is counting on – digitals are not reversed).
3) My test has the power transistor drive an actual load (a light bulb) where the manual version doesn’t drive any load.

(Note: The pin numbers for the following are the ones on the power transistor side connector – not the ones on the harness side connector (for which I put the wire color in parenthesis for reference).

Important: You must use an incandecent 12V light bulb that draws some current, around 1A or more (automotive tester light, taillight, turn signal bulb, brake light, headlight, dome light). DO NOT USE AN LED as this will glow brightly even when you only have 30mA of current flowing. They also are non-linear and have a low turn-on voltage. LED’s also only conduct in one polarity so it’s misleading if it’s backwards.

On a 2g turbo (Note: 2g NT doesn’t have power transistors):
Unplug the power transistor 8 pin connector.

To test the power transistor for cylinders 1 & 4:
Connect the negative side of a 1.5V battery to pin 3 (black wire) of the connector. Connect the negative side of a 12V battery also to pin 3. Connect the 12V battery positive to one side of a 12V light bulb. Connect the other side of the 12V light bulb to pin 8 (black/white). The light should not be on. Now connect the 1.5V battery positive to pin 7 (black/blue). The light should go on.

To test the power transistor for cylinders 2 & 3:
Connect the negative side of a 1.5V battery to pin 3 (black wire) of the connector. Connect the negative side of a 12V battery also to pin 3. Connect the 12V battery positive to one side of a 12V light bulb. Connect the other side of the 12V light bulb to pin 1 (blue/black). The light should not be on. Now connect the 1.5V battery positive to pin 2 (brown/red). The light should go on.

On a 91-94 turbo or NT:
(Note: The pinout is the same as the 2g turbo one but the wire colors are different.)
Unplug the power transistor 8 pin connector.

To test the power transistor for cylinders 1 & 4:
Connect the negative side of a 1.5V battery to pin 3 (black wire) of the connector. Connect the negative side of a 12V battery also to pin 3. Connect the 12V battery positive to one side of a 12V light bulb. Connect the other side of the 12V light bulb to pin 8 (yellow/green). The light should not be on. Now connect the 1.5V battery positive to pin 7 (yellow). The light should go on.

To test the power transistor for cylinders 2 & 3:
Connect the negative side of a 1.5V battery to pin 3 (black wire) of the connector. Connect the negative side of a 12V battery also to pin 3. Connect the 12V battery positive to one side of a 12V light bulb. Connect the other side of the 12V light bulb to pin 1 (yellow/black). The light should not be on. Now connect the 1.5V battery positive to pin 2 (yellow/red). The light should go on.

On a 90 turbo or NT:
Unplug the power transistor 6 pin connector.

To test the power transistor for cylinders 1 & 4:
Connect the negative side of a 1.5V battery to pin 3 (black wire) of the connector. Connect the negative side of a 12V battery also to pin 3. Connect the 12V battery positive to one side of a 12V light bulb. Connect the other side of the 12V light bulb to pin 1 (yellow/green). The light should not be on. Now connect the 1.5V battery positive to pin 2 (yellow). The light should go on.

To test the power transistor for cylinders 2 & 3:
Connect the negative side of a 1.5V battery to pin 3 (black wire) of the connector. Connect the negative side of a 12V battery also to pin 3. Connect the 12V battery positive to one side of a 12V light bulb. Connect the other side of the 12V light bulb to pin 6 (yellow/black). The light should not be on. Now connect the 1.5V battery positive to pin 5 (yellow/red). The light should go on.