My 2001 Mazda B4000 truck was stolen a couple weeks back. The thieves drove it a few miles away to steal the catalytic converters and then ditched it.

Since getting it back I can start it but I now have an issue where when I accelerate the battery light comes on and the battery voltage drops. At idle it seems fine.

Of note, they busted the ignition cylinder so it now turns without a key, but since it uses a transponder key, you still need the factory key for the vehicle to start.

I can't find any cables that look to be cut or have been tampered with.

My question is how did the thieves start the truck by bypassing the anti theft immobilizer? And what in the process of doing so would cause a grounding issue for the voltage to drop when the RPMs rise?.

Cheers,
Justin

PS follow-up question. Anyone in CA use non carb compliant catalytic convertors and get failed at a smog test?

 

Welcome to the forum

Last first
Smog test usually includes a look at exhaust system, mirror on wheels, lol, if any parts look "new" then they will want the CARB sticker for the new parts, and its hard to make new parts look old, lol

You can use a Laptop computer with Forscan or similar Ford software to "add a transponder key" to PATS key list, this is done by just plugging laptop into OBD2 port
Still need to break into the vehicle, and break the lock on ignition, but the "added key" put next to the broken ignition lock will allow start up

But it usually takes 10 to 15min to add keys, its timed delayed on purpose to prevent "fast getaways"
But there are "coded" entry which is faster
Article here on using Forscan to add keys: https://forscan.org/forum/viewtopic.php?t=839


Alternator may just be failing nothing to do with theft
You can test the 3 wires on the vehicle side to see if they are OK

Key OFF
Use alternators metal case as the ground, set Volt Meter to 20vDC, or just DC Volts
Test meter by hooking it up to Battery, 12.3 to 12.8volts is expected, but IF alternator hasn't been working it may be a bit lower

Once meter is known to work put black probe on alternator metal
Put red probe on B+, thats the stud/nut terminal on back of alternator
Should see Battery Volts, what you just tested for
If not then you have a blown fusible link

now unplug the 3 wire connector on alternator
Test the Yellow/White wire
Should see Battery volts
If not then a Fusible link is blown

If so then move to test Light green wire
Should be 0 volts
Turn key ON
Retest green wire
Should now see 12volts, will be a little less than Battery volts, thats OK
If not the fuse 11 in cab fuse box is blown, but unlikely because your battery light works, green wire is battery light wire and the ON/OFF switch for alternator

If all 3 wires test OK, then Plug back in the 3 wire connector, and make sure the short white jumper wire is plugged in to its single terminal

Start engine
Test battery voltage
13.5 to 14.8volts is expected
Under 13.5v would be a failing alternator, replace it
Raise RPMs, battery volts should go up above 14v if not replace alternator

Battery light comes on when alternators Voltage out, drops below Battery's Voltage, i.e. 12.3 to 12.8volts
As you raise RPMs the engines spark system needs more voltage, so if alternator is at or just under 13volts then it will drop lower when you REV the engine