[jmkcc]

Car runs fine but is throwing P0100 open MAF circuit. Tech2 shows zero gps reported by MAF. I have 5 volts at pin 1, pin 2 is grounded and no volts or short to ground in pin 3 (red/green) wire. Working backwards, I do not appear to have power at pin2 of connector H33-5 behind the glovebox. Earlier I checked fuse 16b and there was power to the top fuse leg and the fuse was good. Checked now and no power. Swapped relay 22ish in the under dash relay box. The relay seems to ahve power on pin 30 (big orange wire) and the right hand pin of the relay but not the red/green wire going to the fuse panel.

I have two questions. First - it seems that the red/green wire that goes from connector H33-5 behind glovebox to engine bay is split in the bay and connects to injectors, maf, and other sensors. If that really has no power - would the card still run?

SEcond question - How does power get to connector H33-5 from the engine bay realy/fusebox? Does it go engine fusebox to fuse panel 16b to relay under dash to H33-5 to MAF? Or does it go engine fuesbox to relay under dash to fuse panel 16b to H33-5 to MAF?

I did do a lot of dash work, radio wiring etc so I suppose I could have knicked something in the dash or in the engine bay. I have not seen any obvious nicks to wires or harnesses yet though. And I am puzzled by the fact the engine runs smooth - that makes me think it has to be a break from MAF to whereever the wires are crimped and routed to injectors, maf etc...

 

[jvanabra]

Have you downloaded WIS? The wiring diagrams for Trionic are kind of a PITA to use, but will have that info.


You can also download the T7 docs from txsuite.com - it has a good system overview and will give some clues about what's connected to what, and where power comes from etc.

 

[jmkcc]

Yeah I have WIS and found a few pages with locations/ID numbers and some pages with schematics, but I was missing the schematic page that showed the circuit from the battery to the relay and fuse panel. I found that at lunch so I have the circuit mapped out now.

The symptoms are still a bit strange as the same lead provides power to the injectors, MAF and a few other items in the engine bay. If there was an issue with a fuse, relay or wiring in the cabin I'd think it would impact the injectors along with the MAF.

 

[jvanabra]

Looks like I gotta do some more digging around myself so I'll take a look too.

 

[jmkcc]

I wasted a bit of time working backwards checking for voltage ultimately arriving at the main relay under the dash that provides power to fuse 16b. It finally hit me that the relay did not ground direct but went through the ECU. I left the MAF unplugged as I worked back and I assume the ECU did not like that and would not ground the relay. That kept the relay from switching and providing power to fuse 16bm, connector H33-5, Crimp J?? and ultimately the MAF.

So back to square one after reassembling the dash. Problem must be between the engine bay branch crimp and the MAF. As noted I did not see anything obvious so I might just run a new wire from the junction to the MAF connector and hopefully be done with it.

For the record I'm pretty sure the MAF 12V ignition on circuit is as follows:
1. Battery to Main fuse next to battery in engine compartment
2. Main fuse in bay to main relay 229 - power to terminals 30 and 88 (orange wires)
3. Key on - Relay terminal 85 grounds through ECU pin 26 (blue/gray wire) and powers relay terminal 87 (Green wire)
4. Relay terminal 8 crimps 4 branches at j76 (red/green wires) which power fuses 16b, 26, 38b and fuel pump relay 102 terminal 30.
5. Fuse 16b to connector H33-5 pin 2 behind glovebox (red/green wire)
6. Connector H33-5 pin 2 to engine bay crimp J34 with branch to MAF pin 3 (red/green wire). Other branches from J34 power bleeder valve 321, injectors 1-4 and connector H6-12.

MAF pin 1 blue/gray wire to Trionic pin 65 carrying 5V.

MAF pin 2 black wire to J185 crimp and then ground (I think on intake)

 

[jvanabra]

That seems about right - very, very similar to Saab fuel injection going back to the LH Jetronic days.


I would think this bit:


H33-5 pin 2 to engine bay crimp J34


is where you'd wanna focus effort. I *suspect* you'll find 12v at H33-5/2 and at J34, and then it dies.


You could also just check continuity between main relay #87 and each step along the way - fuse, H33-5, J34, MAF... or between any two other points. I'm not sure where the main relay is, but somehow I suspect it's in that relay box above the driver's feet, that giant unforgiveable PITA.

 

[jmkcc]

After review, the call on the field was changed! The harness was not all good despite the fact that it looked all wrapped up nice and neat. Turns out someone spliced in an 8"ish extension to the MAF and purge valve wires. It was nicely done - soldered, heatshrink and then taped to look like new - but the MAF wire corroded and broke off.

I'm guessing the PO had a performance intake and moved the MAF and purge valve. Whatever. I'm just happy it was simple to find and fix. Would've been even simpler if I dissected the wire harness near the pure valve before pulling apart the glove-box and dash panels...

 

[jvanabra]

Occam's razor?