Anyone ever hear of this. i read about this mode in a camaro repair manaul. it says you can use your SES light as an air/fuel ratio gauge. this is what is says:if ALDL B is grounded to terminal A with the engine running, the system enters field service mode. in this mode, the dash warning lamp will indicate wheather the system is operating in open or closed loop. If working in open loop, the warning light will flash rapidily 2 1/2 times per second. in closed loop, the flash rate will slow to once per second. Additionally, if the system is running lean in closed loop, the lamp will be off most of the cycle. A rich condtion in closed loop will cause the SES light to remain lit for most of the 1 second cycle.

Does this work?

 

It's true.

 

Perform an archive search for "Field Service" and "Vader". You'll probably find twenty five hits on how to do this.