Air Flow Meter/Sensor: Testing and Inspection

WIRING DIAGRAM:

CHART C-13, MAF BURN-OFF CHECK (5.0L)

Due to contaminates in the atmosphere a residue may build up on the air flow meters sensing wire. To maintain an accurate reading from the meter a "burn-off" cycle will only occur if the ignition is turned off while in the closed loop mode and this is determined by the sate of the serial data line (CKT 461). If the engine is shut down while in open loop or the ignition is cycled on to off, the serial data line will be in a high state (about 5 volts) and remain there for about 5 seconds. However, if the ignition is turned off while in closed loop the serial data line will go to about 2.5 volts for 5 seconds. This voltage (2.5 volts or less) is what triggers the control circuitry in the burn off module and causes burn-off to occur. When the conditions are met to activate burn-off, a 3 to 5 second delay will couur. After this delay the control circuitry will cause 12 volts to be applied on CKT 994 for 1 second and this will cause the meters sensing wire to glow red hot (about 1000°F) and the cycle is then complete.
A Code 33 or 34 will set if the airmeter fails and the same circuitry is used for MAF output as for burn off. Therefore the only functional check needed for the burn-off function is to check whether the burn-off signal is reaching the air meter after engine shutdown.

Chart C-13 - Functional Check of MAF Burn-off Control:

In order for the burn-off cycle to function, the 12 volts on terminal E must remain until the burn-off signal occurs. This checks for the 12 volt shut down delay.
2. Grounding the ALCL terminal E causes the burn-off module to activate burnoff. This check will determine if the burn off module and wiring are OK.