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Good note, Bill.
The OBD Diagnostic Test Modes are fully described in the Engine OBD section in the FAQ here. These tests can be a very useful diagnostic aid. People should learn and remember to use them more often. They can help find a non-working device, confirm a suspect device as well as reducing the number of possibilities. They're quick and easy to run, can be done curbside, no tools, don't need work clothes, don't even get your hands dirty.
The DTM 2 sensor test can find a failed CPS causing a cold or warm no-start. It's not so good at finding a failing CPS causing a cutout stall or hiccup, such as a damaged one subject to interference and vibration when running. Among other things, it's good for confirming the adjustment and integrity of the TPS switch, making sure the ECU can actually see the click of a dirty/worn switch.
DTM 3 is also covered in the FAQ which operates a number of ECU controlled devices. The FAQ neglects to mention that it also cycles the later 2 speed electric fan (low/high) as well as the fuel vapour solenoid, so obviously taken from an earlier manual. It's good for a quick check for a bad or disconnected injector or not being able to operate the IAC valve. Also good for exercising a sticky IAC to help confirm it's worn.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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