pcmhacking.net

I have struck a problem with a rebuild. As i want to keep this simple i will for-go the pretext for now.

I believe i need to replace the PIM as im unable to connect to the bus using ALDL, it looks like class 2 data, not idling at 5v even when IGN is off.

My question is, what is the easiest suggestion for replacing the PIM in this day and age.

I believe im seeing affordable PIM's on ebay that appear blanks, although they are advertised for GEN 3. As it's just a proxy and should have the basic framework, im thinking they would be appropriate.

Ultimately any pricing info or options would be greatly appreciated.

Edit: Should mention its a straight v6

The only VT that should have a PIM is the LS1 as the engine computer talks VPW. V6 or 5L v8 will not have a pim and will be straight ALDL.

while i have your attention, could i ask if you understand what is going on, i cant see any predictable 8192 data, voltage is irregular when car isnt in IGN/diag mode.

the tool works fine on the VS and i thought they were practically the same protocol wise.

Are you checking this with a scope? I'd say most likely fault is one of the devices on the bus has died. Most likely options are BCM and ABS. Try unplugging 1 or the other and key on without starting the engine and see what you can see on the bus then. You should see the security requests coming out of the pcm looking for the bcm.

you have given me a great direction, thanks for your responses.

On VT, ALDL (pin 9) connects directly to BCM, thence via a relay to PCM, etc. (Edit: BCM & PCM, thence other devices.)

From memory, when you turn the ignition on, the BCM will open this relay for 5 seconds, thereby briefly disconnecting the other ALDL devices. Observing the ALDL behaviour during this time may give a clue to where the fault lies. (Edit: See below.)

Joe.

replying just for those with general interest.

what i observed when plugged in is a single character being transmitted 13 times (pattern).

Sometimes its 0x4, sometimes its 0xC.

it reminds me of a capacitor somehow impeding on the line, very superficial but appears to have logic because of expectation and pattern.

when the car is switched to IGN, the same character is being transmitted, but varied lengths between a sizable pause in communications line.

everything else is working, when i confuse the BCM the PCM will switch the radiator fan to suggest the break down.

I've read somewhere that ABS modules are known to fail and disrupt the ALDL data bus. Don't know how true that may be.

Did you monitor the ALDL data line with a voltmeter directly after turning the ignition on, looking for a 5 second change?

Joe.

- i have disconnected all modules and repeated tests (both fuse and plug methods)
- pcm serial line voltage is 1.8v steady, bcm + pcm is variable even when ignition is off
- no predictable aldl communication even after IGN is switched
- no noticable scorching on the board

given the board doesnt have alot of capacitors, im thinking its the crystal/rf receiver thingie or a voltage regulator, but nothing noticable.

time to throw in the towel and get a mobile mechanic out to resync some repurposed stale cake (bricks for paper weights me thinks)

Methinks the PCM is stuffed. "1.8V steady" just isn't sensible, it should be 5V if the other modules are disconnected (and the PCM is properly powered). I'm assuming there's an internal pull-up resistor, like in earlier PCM's. As for ALDL activity when the BCM is connected, ignition off, apparently that's normal for a VT (yeah, as if battery drain wasn't bad enough already!).

Also, I need to correct what I said previously about the 5 seconds ALDL disconnection thing for VT(+), it's a bit more complicated ... firstly, the PCM is hard-wired to the BCM, it's all the other modules that connect via a relay; secondly, you'd need to induce VATS failure, say, by placing some insulation on the key reader slip ring.

Joe.