[07Versa6MT]

Does it try to fire at all? Were you using one of the original keys that came with the car? It's most likely a NATS (Nissan Security) problem, i know once in a while for no reason at all (that i have cared looking into because it happens so infrequently) i will get a no start too. Usually if i get that i take the key out for at least a few seconds then try again and it works.

From my educated guess, i would imagine the NATS is just a series of modules that are tacked on to the regular body wiring/control modules meaning that if this is a common problem, the component failures are probably across the entire line. I've actually replaced a few BCM's because of either this NATS problem, but usually more often than not they have a car that seems like it's possessed as well (random unlocking/locking, power steering motor stop working, warning lights erratically on/off). It may be the receiver unit/antenna that sees the key fob or key chip signal and enables or disables ignition accordingly. Not sure if the older Nissan keys have chips in them.

Diagnosis of electrical gremlins like this should be done by a tech that can actually pinpoint the problem. All too often you get techs at dealers just throwing parts at the issue. It could be in the IPDM, BCM, or the NATS module... All will probably be expensive to replace.

The dead battery issue is likely separate and this is just coincidence. Things you need to know to diagnose that is how old was the old one (was it factory original?), were you getting any symptoms prior (alternator growling, battery light in dash, slow cranking)?

Unfortunately with modern cars, CPU's control alot of circuits and the functions those circuits perform, and when they go bad (the one in the IPDM for example) they cause all sorts of haywire behaviour, and at that point if it's been pinpointed to a module (CPU) causing the problem then there's nothing else to do but replace it.

 

[07Versa6MT]

You've been driving for a month with your Check Engine light on and haven't had it checked?:surprise

If it's not causing driveability issues why bother?

 

[07Versa6MT]

I'm a mechanic, you don't need to patronise me with all that.

Too many mechanics don't check wire circuitry, the stuff that's actually verifiable, before jumping to a module. Modules are always expensive. A few manufacturers haven't seem to have gotten good CPU/module/PCB suppliers, or haven't gotten engineering down right the first time. I can understand a PCM going due to heat from injector drivers etc, but not erroneously at low mileage.

You could pinpoint the parasitic load/drain on the battery yourself if you have a DVOM, hook it up on milliamps in series with positive terminals, and start pulling fuses until you find the affected circuit/group of circuits.

 

[07Versa6MT]

IPDM controls the timer for the lights shutting off. I think part of the problem is that the IPDM is in a particularly bad place where water can leak past. It's in the engine bay on the left side in front of the strut tower, right above the fender liner. Corrosion is probably a big reason why these fail and start causing haywire. The IPDM integrates one big CPU controller, and the function of individual relays in a traditional relay panel. Unfortunately it seems to be less reliable than traditional relays. At least with individual relays you can replace the problem ones, whereas the IPDM is non-serviceable. So if one circuit controller is problematic you must replace it as a unit to fix one problem.

There are certain things in a computer on cars that is stored on what i would call "hard memory", or memory that doesn't require power to sustain. Same as when you put your computer to sleep vs hibernation, sleep puts all the data required for your current state onto RAM which requires power to sustain, whereas hibernation puts it onto a hard disk or solid state drive which doesn't require any power at all to sustain. Much like the odometer data will never leave that vehicle if it loses power, the key stuff is the same. I think it's a NATS module or maybe the receiver acting erraticly that's causing intermittent locking/unlocking issues. Perhaps due to corrosion or bad connections internally, or the CPU/PCB itself.

Jim, i know it's not recommended practice to just drive around with a CEL, but if the customer knows what it is and that it is not affecting anything then it isn't a problem. An H02 sensor code CAN cause poor fuel economy, CAN... it depends on what specific code he has for it. Is it just an O2 sensor heater circuit? Is it the A/F wideband that is a direct feedback to the ECM? Or is it just the post-cat narrowband sensor that simply monitors post-cat gasses and triggers a code based on cat efficiency? Even then, a cat-efficiency (or rather de-fficiency) code is not necessarily grounds for cat replacement, often it is an incorrect A/F caused by something upstream (vacuum leak, incorrect fuel pressure at the rail, clogged injectors or sticking injector pintles). In the case of incorrect A/F, STFT (short term fuel trim) value is a very good way of determining if there's a problem in the fuel delivery or management system.