Reading engine management light codes

jsmoke

jsmoke

jsmoke

Soldato
Joined
17 Jun 2012
Posts
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Can you do this yourself, I see you can buy scanners etc for around £20, are they as good as what a mechanic would use. Is it as straightforward as getting the code then looking it up?

From what I can make out it may not be that simple?
 
Aye, a £20.00 scanner is as good as the ones costing £100s/£1000s that a mechanic would use.
 
Got a smartphone? Get an OBDII reader suitable for it and download something like Torque. It will let you see the codes, and even clear them (if you are sure you know what it is and the cause)
 
If you want to clear codes not all can do them.

I tried a few cheap ones for my Alfa and certain lights they couldn't clear. Think some errors need more specialised software.
 
What our friend meant to say, I'm sure, was that they are good for the basics. The OBD2 standard provides access to most basic error codes a car can throw. Where you pay the extra money it allows you to access specific modules in the vehicle and view / adjust values. For example using INPA on a BMW or VCDS in a vw/audi group car will allow you to see absolutely everything. From individual wheel speed sensors to climate controls and everything inbetween.

A generic OBD just lets you read (and sometimes reset) generic OBD information.
 
I wouldn't be without one, but a generic code reader is only semi useful. Sadly they often will simply throw fairly generic fault codes which are no use on more complicated cars. Mercedes for example you will be lucky to really get much from a regular reader.
 
Jez said:
I wouldn't be without one, but a generic code reader is only semi useful. Sadly they often will simply throw fairly generic fault codes which are no use on more complicated cars. Mercedes for example you will be lucky to really get much from a regular reader.
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So what one do you have and why would you clear codes, surely you need to fix the problem first?
 
It really depends on the car, i've got a generic elm327 bluetooth one with Torque on my phone.

It only gives fairly generic codes but with a bit of googling you can usually figure out what it's meaning, it will normally let you clear the fault as well.

This is useful if as an example i had an engine light in my old Subaru, turns out it was one of the O2 sensors, nice and easy DIY fix so i replaced it and reset the light myself.

With modern cars they can be a bit useless as it may not even show anything if it's not a standard ODB fault and could be in some other module in the car, that's where the posh scanners come in as they can properly communicate with all the different modules in the car.
 
It depends on what car it is and what modules you want to access. For example a cheap generic tool will likely only read global codes and not manufacturer specific codes, it is also unlikely to reset certain things like SRS codes etc.

The cheap tools or things like Torque etc are great to have though.
 
I bought a cheapy one by VIDENT - orange with colour screen but not the cheapest one in that range - seems to work pretty well for what it is automatically identified all vehicles I've used it for so far and has enough information for non-professional use.

If you (in general) need more than it provides then you probably wouldn't need to be asking about the reader heh.
 
jsmoke said:
So what one do you have and why would you clear codes, surely you need to fix the problem first?
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The generic ones all output the same stuff, I just use an old work phone combined with a Bluetooth elm. It has been useful a number of time on various cars, it at least gives some idea of the problem and allows you to reset the EML once you think that you may have fixed an issue.

As I say though, on more complex cars they are not that useful. I have an e class cabriolet which threw an EML and went into limp mode. The generic reader gave a code out, but it was a generic manifold code which could have been anything. Off to the specialist it went, to go onto a proper STAR machine which diagnosed a couple of issues instantly.
 
The cheap ones generally show only engine related codes (no SRS, PAS etc..) and only the generic OBD2 codes, nothing manufacturer specific. Sometimes that's enough to track a fault down, other times it can be pretty useless.
 
jsmoke said:
So something like this?

https://www.amazon.co.uk/Torque-Pro...&pf_rd_p=2c00cff3-944d-5bb4-a4cb-89f3cf303857
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Got this exact one as well, i just leave it plugged into my car. It was good to see how often the DPF was regenerating.

The idea is to clear off the current fault codes and then drive it about/wait for problem to reoccur and check what fault codes are present. The problem with cars is that they have a lot of sensors, and some will trip for absolutely no reason at all, leaving a load of false positives on the fault code list.
 
Semple said:
Got this exact one as well, i just leave it plugged into my car. It was good to see how often the DPF was regenerating.

The idea is to clear off the current fault codes and then drive it about/wait for problem to reoccur and check what fault codes are present. The problem with cars is that they have a lot of sensors, and some will trip for absolutely no reason at all, leaving a load of false positives on the fault code list.
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Multiple faults can point to a problem elsewhere.

EG, A problem with a supply rail feeding multiple sensors will trigger fault codes in all those sensors even though there might not actually be anything wrong with them.

This is where circuit diagrams come in handy. Though it can be hard to track down accurate ones

(The standard Haynes manual wiring diagram with the word "Typical" in the title isn't really much use!)
 
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