Wiggle test. -Why a check engine light is there.

A wiggle test is not high tech, but any good technician (or survivalist) should know what and why its done,some do not. The check engine light is a diagnostic indicator.(I'm not talking about flash codes) several dealer techs don't know a key on light test. Post collapse, you may need to know.

In days of old, before I was stripped of my civilian rights, and I could work for a living keeping what I made less taxes..........Now they take so much a job with deductions, and garnishments isn't worth going to, it costs more to drive there. Besides having the cops calling your co workers telling them you have a warrant to answer too, Doesn't exactly promote peer respect. ( I made the life changing mistake of sleeping with my teacher I was 16 she was over 38. It totaled 200k in CS. Half was interest for the state. I still owe 75k. It costs my life and my future and every thing I own. The USA justice system is crooked. She was going to go with adoption but decided she would rather have the child support and got welfare for 12 yrs.) ( a gold mine for her a shaft for me)

Anyways back in the day I worked on industrial and heavy equipment factory comparability component diagnostics.(High Tech Mechanic) I have solved technical issues of many types of equipment you see every day. My findings were reported to design engineers and influenced design changes. Basically when new designs are introduced to the market, design and comparability problems arise.

Here is the scenario: My wife and I were driving our cool car down the road. Actually she was driving, I had already had several drinks, we try to be legal when possible. Anyways we turned the corner and the car died. The lights were still on same with the radio. The starter would crank, but engine would not re-start.

Since the lights and starter work you know you have power and plenty of it. The problem this far is quickly narrowed to either: Fuel, Ignition, or Internal engine. Most vehicles these days are computer controlled. The computer is a plus. It can serve as a quick diagnostic tool that's hooked up and ready to work for you. (Its fair to note in an EMP scenario your,  screwed.) ( also if your at post-collapse and  being chased by a hoard of angry bikers, when the failure occurs, you and the wife will likely get screwed) I'm writing this post on the assumption you do not want to get screwed by a hoard of bikers........, but maybe the wife..... Na, never mind,,,,,,, lets assume (for discussion)  both do not wish to get bent over the disabled vehicle.

A vehicle check engine light, when working properly is supposed to come on when the key is turned to the on position, and will remain on for usually 3 sec. (depends on make) Then it should go out. This is a self check. When the light goes out the system has completed the self check, and has passed. If it flickers and stays on there is an active fault. (still may run). If the light does not come on (at all) when the key is first turned on, this is your problem. The ECU (electronic control unit) does not have power.It will not run! (the remote possibility exists that the bulb is burnt, or the wire to the bulb is failed. This is not going to be the cause. The light worked before it will work now).

I have seen experienced technicians in the field spending hours working on things with-out doing the key on test. I remember several times they have spent 8 or more hours working, only to haul it in, to the shop and find the fuse to the ECU is blown.( transporting equipment ranges in the 2k price at minimum, cars are of course cheaper but it sucks when it didn't need to happen) Here it is again turn the key on, The check engine light should illuminate, then go off. If it comes back on that's another deal. If it does not come on at all, it will not run, It does not have power to the ECU. Check fuses then wiring to ECU. Its that simple.

I just remembered. I was looking at a car for sale at a car lot it was in the shop when I stopped by to look at it. The mechanic was there (lurking) I turned the key on and noticed the check engine light did not come on. It did start though. When I mentioned it to him. He thought it wouldn't come on if there weren't codes. (moron). I suspect it has codes he didn't want to fix or couldn't. And disabled the light so it wouldn't get noticed. So always check the light when shopping for a car.

Back to the wife and I. We were on a country road (no bikers in sight) I turned the key off then back on. The  check engine light did NOT come on. I popped the hood and checked the fuse to the ECU, it was ok. I tried the key test again, The light came on then went off. I tried to start it and it started. Clearly there is a bad connection somewhere, relating to ECM power.

Do you see the value of this test? All this took perhaps, 1 min. from stall to restart. If a person didn't know they would be looking for fuel psi, engine problems or a spark to name a few. If this test were not preformed a person wouldn't have a clue where to even start to look for a bad connection, especially when the connection  comes and goes.

This self check light works  on just about everything, from heavy equipment, to cars, and over the road freight trucks (semi-truck).

Remember, the car is still not fixed. Its running so we just drove it to our destination. But because of this test I know just where to look. The light did not come on when it wouldn't start. So I know there is a problem with power supply to the ECU (no light no power). There are no other causes.

A wiggle test is a good way to find problems with electrical things when they work sometimes and sometimes don't, intermittent short. The fastest way to find this is by wiggling wires and connections related to your circuit needing repair till you find a spot that duplicates the failure. In the case of my wife's cool car, I wiggled the harness to the ECU and right off found a poor connection at the plug-in connector in the wire harness to the ECU. I repaired the wire. All this took less than 5 min. If it were not for this test a repair could literary take days and lots of money in a shop. I've seen it happen. Remember if it just shut down and after a while it would restart, a person would have no idea where to start looking.( the possibility are endless) With electrical the diagnostics is the expensive part. The repair is easy, Knowing the how and why, makes the diagnostics easy.