Testing the transmission range switch (known in non-Honda tech speak as the PRNDL switch or park/neutral safety switch) isn't hard.
You don't need any fancy/expensive diagnostic tools to do it... since the tests only require a multimeter.
This tutorial will help you check the continuity of the different circuits that make up your Honda's transmission range switch.
Here are the contents of this tutorial at a glance:
It's rare for the transmission range switch to go bad on its own. Most, if not all, of the transmission range switch problems I've diagnosed/repaired have been due human error causing the failure of the switch.
To be a bit more specific... the automatic transaxle (the correct name for a FWD transmission) was removed and the sensor was broken/damaged in the process.
The most common symptoms you'll see when the transmission range switch (PRNDL switch) fails are:
The transmission range switch is part safety device and part PCM sensor (PCM = Powertrain Control Module = Fuel Injection Computer).
The safety device part of the transmission range switch ensures that your Honda cannot be started unless the transmission is in neutral or park and thus prevents the your Honda from moving immediately when it is started.
The sensor part of the switch tells the PCM in what gear the transmission is currently in when you turn the key to the on position or start the engine.
The transmission range switch is know by several names:
Alright, let's get testing...
Testing the transmission range switch simply involves checking the continuity between certain terminals of the switch with a multimeter.
Using the illustration below, I'll give you an example. Let's say that you want to test the reverse light circuit of the transmission range switch. You would:
Interpreting the results: If you're multimeter registers continuity in the circuits... then the transmission range switch is good. If the multimeter DOES NOT register continuity... then the transmission range switch is bad and needs to be replaced.
“A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.”