Holden Commodore Pricing and Specs

The answer is probably a pretty simple one in terms of what’s causing it. The warning light is to remind you to leave the car with Park engaged. So, the gear selector will have a tiny sensor or micro-switch that detects the selector in the Park position which is then conveyed to the car’s body computer. But if the sensor or switch is faulty or not adjusted correctly, the computer will think the car is not in Park and will light up the warning to alert you. The intermittent nature of the fault is what makes us think this is the case, combined with the fact that a quick flick of the T-bar button is enough to make the warning disappear.

So much for the cause, because the fix might be a bit more complicated. Depending on where the sensors and switches live, you may need to disassemble more of the car than would seem necessary to fix such a seemingly small problem. An auto electrician should be able to make sense of it.

A manifold leak will throw the engine’s fuel-air ratio out the window and can cause poor cold running and hard starting. The old school way of checking for a vacuum leak is to get the engine idling and then spray either carburettor cleaner (or something else flammable) around the intake area of the engine. If the engine suddenly picks up revs, you almost certainly have a vacuum leak. But be careful, spraying flammable stuff around a running engine comes with a fire risk.

The other thing to check would be the throttle body and the sensor attached to it that tells the computer how much throttle has been applied. Again, these can start to give false readings, throwing the fuel-air mixture out.

Before you do either of those things (replace the engine or the whole car) find out where the coolant is leaking from. You might find that it’s a simple case of a leaking hose or a worn out water pump that is causing the leak. If that’s the case, it could be fixed for a few hundred dollars or perhaps even less. Even if the problem is a rotted welch plug or a blown head gasket, the cost to fix it won’t be anywhere near as high as replacing the engine.

On top of that, you know the history of the engine you have, while a second-hand engine can be a bit of a lucky-dip: You might get a good one, you might not.