Not long ago, a garage tried to charge me £80 (plus vat) for connecting my car to 'the computer' to tell them what the problem was!

I knew what it was already. The alternator had packed up. In the event I walked out, and got it replaced at a specialist company. Problem solved!

But it set me thinking, and I have since bought a bluetooth dongle which connects to the car's diagnostic connector, and interfaces with my tablet. This cost £5. I also bought, for £2.95, an app called 'Torque Pro' which allows the tablet to read all sorts of interesting data from the engine via the dongle. It can reset the fault light, read fault codes and explain their meaning, and monitors all sorts of things from coolant temperature to the output from oxygen sensors, rpm, throttle position, horsepower from the engine, etc. etc. and using the tablets GPS you can see how it behaves on a journey. I suspect it will be useful to check on what garages claim is the problem, and I will quickly recover my investment of £7.95.

There is a free version of Torque which presumably has some limitations compared to the 'pro' version, but as you can see I am something of a spendthrift!

You can buy dedicated plug-in scanners for doing this, but it seems to me that this is a probably the best way to see what your engine does, as well as being the cheapest. There are many other 'apps' which do much the same, many of them free, but I have no idea if they are better or worse. Torque Pro seems to me to do the job brilliantly!

Depending on the sophistication of the car, you can also monitor things like the ABS system, the aircon, and whether your electric windows are working properly!

All for under £8!

Where did you get the dongle from

You can get them off Ebay. Just search ELM327.

To be honest they're a bit hit and miss. I do Peugeot diagnostics and used an ELM on my car. It didn't show any faults.

But once I plugged in the Peugeot-only diagnostic equipment it picked up glow plug faults and a fault with the EGR valve.

Same on my brother's Civic. It had an engine fault and an airbag fault and Torque didn't pick up anything.

We also get a few "home diagnosers" come onto the Peugeot forum, armed with their fault codes but with no idea what they mean - sometimes it comes up with "manufacturer specific code", or what to do with them.

Interpreting fault codes is a skill. I'm sure I've mentioned before about how a certain breakdown company told a customer of mine that his high pressure fuel pump had failed and would be looking at over £300 for a new one, because that's what the fault code pointed to.

And indeed there was little fuel flow at the high pressure pump. But it wasn't the HP pump, it was a fault with the lift pump in the tank. It had run long beyond it's designed life - 16 years and 160,000 miles, and the in-built filter was clogged.

I use a autodiagnose machine it's good but sometimes I need a second opinion

Turnips Dad - Andy (Gibbo) is spot on. The code readers need skill to interpret what the meaning of and the reason why a code is evident. all too many just rely on the reader to tell them the failed component instead of using it to point the way. Many times the reader will give a true indication of a failed component but how many times have we heard about situations were parts have been replaced due to the code reader indicating a particular item yet the problem remains. if its a generic reader care is needed and it is best used as an indicator in the first instance followed by further diagnostics. Specific code readers such as VagCom and the code reder Andy refers too are manufacturer specific and are more likely to isolate the failed component accurately; that said I have used the Snap On Modus and I have a generic reader which is an Autel, the Autel has been very good in my diagnostics but I use further diagnostics too confirm a fault. Gone are the days when I used the Crypton tuner with the Lab Scope facility to measure signals from sensors, not sure if that's a good or a bad thing though!!

The problem, I think, is that there are manufacturer-specific codes which are not published.

Torque pro happily reads generic codes, even those which do not trigger the engine light, but if they are manufacturer's codes you are on your own.

It is true that you need to be understand what the data means too, and to interpret what is causing the fault. (I am no expert, so many of the sensor outputs are pretty meaningless to me.) There are books on this which may help but I have yet to buy one as they seem to be written for the US market not the European one, and or very expensive. Perhaps someone might like to recommend one if they know of a good one.

In the meantime, I have been logging and graphing things like coolant temperature over short journeys - I have a Ka which overheats with a sudden dramatic surge in temperature from mid 90C to 130C a few minutes after I have stopped and switched off the engine. This triggers the temp warning lamp if I then try to drive off, but within a minute it goes off as the temp returns to mid 90s. There is plenty of coolant, but apart from that I don't know if it is something I need to worry about. Torque pro isn't going to tell me anything of much help! No fault codes at all are found.

Incidentally, I bought an Autel MS509 before taking the torque route. It seemed to work reasonably well but turned out to be a counterfeit. I couln't update the software, so it got sent back to Amazon who refunded the cost (Counterfeits have a serial number MS505245, and do not update properly)

I suspect a geuine Autel one works a lot better, but cannopt say for sure. I am quite pleased mine was a fake though as otherwise I wouldn't have found the Torque approach, which is much cheaper and does a lot more.

I don't think its that they're not published, more that the software just doesn't have the capability of storing every single code for every single make of car.

The codes aren't secret, there are plenty of websites out there with the code details listed.

On the Pug forums we often get new members signing up saying they've used a generic scanner on their car and got a result "of manufacturer specific fault code".

But if they'd type "Peugeot P1351" for example, into Google they'd have their answer.

As for your temperature issue, have you tried changing the sensor?

I haven't tried changing the sensor, as it seems to be working. It behaves rationally most of the time. I can read, via the scanner, that the temperature rises from ambient when I start the engine, the temperature then remains constant +/1 a degree or so, with the fan switching on and off to keep it there. It is only several minutes after the engine stops that there is a surge in temperature. The overtemperature light comes on when this happens.

The car seems to work OK apart from this. It is a mystery rather than a serious problem.

Authorised garages have an in line box of tricks called a candy, with dealer specific codes which are constantly updated.It allows you to go further into diagnostics than a stand alone tech, if you have one of these outside the realms of a dealership the chances are it is illegal.

I suspect that ALL fault codes can be read by even cheap scanners. The meaning of the manufacturer specific ones is probably available too.

However there is nothing to stop any manufacturer storing all sorts of other information in a database in the engine computer, and of interrogating it via the ODS2 link. I imagine that will not be published. There may even be additional sensors in the car which are not publicly mentioned. Much of this information may not need to trigger the engine light or even result in a stored fault code.

There may also be links to subsidiary processors in the ABS system, the dashboard, the Aircon etc, and all of these will be available to the manufacturer too.

The software to interrogate it and interpret it will be available to the garage, but this will perhaps suggest tests such as revving the engine but will terminate with some recommendation such as "Replace DPF" and very little information as to how it has arrived at this conclusion or what data has been collected will be apparent to people in the garage, let alone anyone else.

In short, what you can get from the ODB2 socket with a simple scanner is far more limited than what a main dealer has.

nope, basic obd can miss loads of faults.

A basic scanner is not going to identify the problem. The best it can do is to read any generic DTCs in the EMU. Interpreting these and deducing what has gone wrong is up to you.

I can't see any reason for it not to be able to read ALL generic DTCs in the engine computer though, and probably a lot of the manufacturers ones too.

go for it then and buy a cheapy obd reader, be interesting though as to prove your theory every time you use it you'll have to use a 'proper' reader to make sure yours hasn't missed any codes

cheap obd readers are cheap for a reason.

Cheap readers are cheap because they lack display facilities and use a low powered processor. You can expect them to be slow and to be less capable of displaying data as graphs etc. They are also unlikely to provide a connection to your computer, and may be flimsy and poorly made. The software engineer who wrote the code inside it would have to do MORE work to stop it displaying some DTCs, as you suggest, than displaying every DTC offered by the EMU. Why should he bother?

I have already bought a bluetooth dongle. (£5) This acts like a piece of wire connected to my tablet (or smartphone), on which I can put any software I choose. My intention is to read every sensor continuously, and store this in a database in the tablet. I can then read this and relate it to what the car is doing on a journey. Torque does a lot of this anyway. If I can't find software that does what I want, I will set to and write it myself. So I don't anticipate having to buy anything more expensive.

For the price its always worth it for messing around with, especially if you want to make up your own custom display to show the advanced data, but from my experience with them about how they didn't pick up faults (posted above) I wouldn't trust them alone for diagnosis.

On more thing, make sure that your car doesn't have a permanent live on the OBD port. I know someone who fitted a dongle and didn't realise it was "on" all the time and it flattened his battery.

It IS permanently live, but the current is very low - about 30 milliamps. It's worth removing of course, but unlikely to flatten the battery very quickly.