code 34, even after replacement

[f85gtron]

I found these instructions online. Does anyone have any words of wisdom or advise and tricks to try and eliminate code 34 from being consistently (and persistently) thrown by the ecm?

"If you have a mulitmeter:

1. turn the ignition to RUN (engine stopped);

2. unplug the MAP sensor;

3. check the voltage between terminals A (blk/red wire) and terminal C (grey wire) in the harness connector;

a. if you get 4V - 6V then that narrows things to either the light green wire or the ECM. To check for an open circuit (infinite ohms) or a short circuit (zero ohms) on the light green wire, switch your multimeter to the 20 ohm range and touch one meter lead to a good ground, and the other to the green wire. If you get either infinite ohms or zero ohms, then the green wire or the ECM is faulty;

b. on the other hand, if you get less than 4V in step 3, turn off the ignition, and check for an open circuit or a short circuit on the grey wire. If you get either infinite ohms or zero ohms, then either the grey wire or the ECM is faulty."

Ron

[Roger]

In step 3a; do not check for ohms with the ignition on.

[f85gtron]

Roger, Roger.

[f85gtron]

I found this image online of vacuum vs volts/ohms online. Maybe this will help somebody (and me too) 

[Roger]

Sorry. That's not Volts vs. Ohms.

That graph shows the relationship between the output voltage of the sensor to the vacuum it reads.
Remember, it is being fed ~+5 volts; therefore, the output voltage will be low at idle and high at WOT.
So, the more vacuum you have, the lower the voltage and vice versa (lower vacuum=higher voltage).
This is the voltage being sent to the computer.


MAP/pressure sensors
There are several varieties of pressure sensors from GM: Map sensors in 4 varieties (1 bar, 2 bar, 3 bar), and a barometric pressure sensor. 1 Bar sensors are good for NA engines, they measure from 0 (vacuum) to approximately atmospheric pressure. A 2 Bar sensor is good for 15 PSI of boost, and a 3 Bar unit is good for 30 psi of boost.
They all share a common pinout, although the connector keying may be different:
•   Pin A -- Ground
•   Pin B -- Sensor output
•   Pin C -- +5 volts

Version   Part numbers                                                                   Description

1 Bar   •   GM part # 2503679  •   standard part # AS-5     Pretty much any normally aspirated TBI GM car, plus plenty of others

2 Bar   •   GM part # 16009886  •   Wells part # SU-129  •   standard part # AS-4     91-93 GMC Syclone & Typhoon 4.3 turbo
                                                                                                                                                87-90 Pontiac Sunbird Turbo 2.0
                                                                                                                                                84-86 Sunbird (actually any J-car) turbo 1.8

3 Bar   •   GM part # 16040749     

Baro   •   GM part # 1600683                                                       Has a piece of foam over the pressure port.


I have other info but it is copyrighted and I cannot post but will email to you.

[f85gtron]

In that case, i hereby retract my claim that the graph in question referenced ohms.
Thanks, Roger.  I've got the idea of it now. I've got some testin' to do. I will report back as soon as my wife will allow.

[f85gtron]

I checked for voltage at the sensor last night at the light green wire (middle wire). It produced the correct voltage at each test point, using a vacuum pump, so it looks like I'll be chasing down a wiring issue.
I suppose the next step would be to test for voltage and continuity at the ecm?  That's the next logical step, right?