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Questions tagged [diagnostics]

Use this tag for generic questions related to tools, techniques and methodologies for diagnosing problems. Do not use this tag for case-specific problems, the "troubleshooting" tag is better suited for that.

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16
votes
3answers
11k views

How can I tell if I have bad cats?

No, not that cat! Catalytic converters - or "cats" - have a nasty habit of failing with age. What are the symptoms associated with a cat that's gone bad? Are there any tests that could definitively ...
12
votes
1answer
3k views

What exactly are fuel trims?

What is meant by the term "fuel trim"? Why are they so important in diagnosing engine operation issues? How do short-term fuel trims differ from long-term fuel trims?
9
votes
2answers
2k views

What is the “propane test” and how is it carried out?

This test is often mentioned in the context of figuring out what's wrong with a car engine's operation (misfires, hesitation, poor fuel economy, etc.) What is this test and what does one need to ...
13
votes
10answers
95k views

How can I detect vacuum leaks without access to a smoke machine?

In the course of helping my friend sort out a lean condition with his Mercedes GLK280 we have to pinpoint the source of a vacuum leak in the intake plumbing. The interwebz tend to recommend having ...
6
votes
2answers
25k views

How can I test my thermostat?

How can I tell whether a mechanical thermostat works as it should? Is there a test that can definitively tell me if a thermostat is good or bad?
6
votes
4answers
20k views

Technique to test an alternator - fact or fiction?

A friend explained that the following is a simple way to test an alternator to see if it is working: Turn on the vehicle. While it is running, carefully remove one of the 12V battery leads. See if ...
5
votes
4answers
6k views

How to Test an Ignition Coil with a Multimeter

I have a 98 Mazda 626 GF and I'd like to test the ignition coils with a multimeter to see if any of them are starting to fail. The car has ECU controlled timing / ignition and there are two coils, ...
18
votes
4answers
9k views

How to test a clutch

I have just bought a second hand car, and I have the feeling that the clutch is worn out. How can I do a quick clutch sanity check?
17
votes
3answers
67k views

How to test for defective glow plugs?

On a diesel engine, how can I know which glow plugs are defective, and can I change these only?
8
votes
1answer
4k views

How to check if spark plugs are firing? Coil-on plugs

While trying to diagnose a tricky car not starting problem I was asked to check if the spark plugs were firing at all. I've found plenty of resources on inspecting the condition of spark plugs after ...
6
votes
2answers
4k views

Is this the correct procedure for a stator test?

Stator Test I have a 2007 DL 1000 V-Strom: I followed the following process while checking the stator: Put multimeter to VAC Tested the three phases of the stator connector plugged into a new ...
1
vote
2answers
1k views

OBD-II Fuel type and level of Monofuel Cars

I'm making an application like Torque and i have some issues with commands of Fuel Type and Fuel level with cars that use only one type of fuel like, Only Diesel or only gasoline. With car Bifuel ...
20
votes
2answers
2k views

What possible causes for the “check engine” light can I check for myself?

The "Service Engine Soon" light came on yesterday and isn't going away on its own. The car drives fine, no weird noises, smells, or other symptoms. The manual is not very helpful, just directing me to ...
15
votes
3answers
4k views

Afraid to crank engine - how can I tell if my cylinders are flooded with water?

Backdrop We had really heavy rains here today. I was in my '99 M5, idling in traffic when I noticed the brake pedal feel became really notchy. When I let go of the brakes the pedal would not travel ...
5
votes
2answers
3k views

P0300, P0302, P0303 on 2003 Honda Civic 1.7

I'm in the process of helping someone with their 2003 Honda Civic, 1.7L engine, 161k miles on the clock. Pulling the codes from the vehicle I got three specific codes: P0300, P0302, P0303. The codes ...
5
votes
3answers
2k views

Testing radiator fan

I took the fan out from my engine compartment and am now ready to test it. It consists of two fans, one larger than the other connected I believe in series with two large wires, one red, one brown ...
4
votes
2answers
2k views

What controls O2 sensor/lambda cycling?

I just replaced the lambda on my 98 Mazda 626 GF 2L because it was showing a signal that was constantly pegged lean and I suspected it was defective. After replacing the sensor I took the car for a ...
4
votes
2answers
5k views

Is there a diagnostic that can be done on a used hybrid car's battery pack?

I'm looking at a used hybrid Lincoln MKZ with 70k miles. The manufacturer provides an 8-yr/100k mile warranty on the hybrid system, so I believe I should still be covered until 2019. I've read that ...
1
vote
1answer
122 views

Skoda Fabia 2005: what I need to know to buy a diagnostics machine?

I'd like to buy a diagnostics machine for my Skoda Fabia 2005. My issue is I'm absolutely newbie on this. I don't know which cable connection requires, if there's some standard, ... Will you provide ...
0
votes
0answers
47 views

Nissan Qashqai “Test Mode”: What does the data mean?

I learned about a "test mode" for the display, which can be used for diagnostics, without an obd reader. I managed to get inside the test mode, but I am baffled by the data and am not sure what it ...