GM Testing - Snap-on

Chapter 8 <strong>GM</strong>
<strong>Testing</strong> Control Systems Tests (Except ABS)
FUEL PUMP RELAY (ON/OFF)
ON OFF CHANGE DATA PRESS N TO EXIT
RPM______________850 TPS(V)__________1.25
TPS(%)____________23 ADAPT SHIFT CNT__OFF
Figure 8-44 Sample Fuel Pump Relay Functional Test
Variable Control Test
Figure 8-45 is an example of a typical variable control test.
CANISTER PURGE (%) 0
>TEST SCROLL DATA CHANGE LIST EXIT
RPM_____________630 TPS(%)_____________0
EVAP PURGE(%)____30 EVAP VENT SOL____OFF
Figure 8-45 Typical Canister Purge (%) functional test screen
Selecting TEST from this screen changes the display to show the commanded duty cycle of
the Canister Purge solenoid as a percentage, starting with zero (Figure 8-46).
CANISTER PURGE (%) 0
*0 SCROLL DATA CHANGE LIST EXIT
RPM_____________630 TPS(%)_____________0
EVAP PURGE(%)_____0 EVAP VENT SOL____OFF
Figure 8-46 Typical Canister Purge (%) functional test screen
NOTE:
i Some variable control tests, such as command gear, require a press of the Y button to confirm
each variable value change request.
During a variable control test, scroll to increase or decrease the variable control value. In the
above example, scrolling instantaneously changes Canister Purge solenoid opening by
varying the duty cycle in increments of 10%. The duty cycle commanded by the scan tool also
appears in the upper right corner of the screen (Figure 8-47). Other variable control tests act
similarly.
CANISTER PURGE (%) 10
*10 SCROLL DATA CHANGE LIST EXIT
RPM_____________630 TPS(%)_____________0
EVAP PURGE(%)____10 EVAP VENT SOL____OFF
Figure 8-47 Typical Canister Purge (%) functional test screen
EGR Control
NOTE:
i Since a proper Exhaust Gas Recirculation (EGR) system operation is crucial to preventing a
vehicle from emitting high levels of NOx, the EGR control test is described in detail here.
158