make sure the harness at the pump module is clean and fully seated. also make sure it's grounds are good.

 

Candi module is for CAN bus, only required for 08/09 and maybe not at all for AS.

Disconnect the battery for a few minutes, this will reinstate communications should the vehicle have powered up with the AS Unit connected.

Possible issues:-

• Break in the Serial Comms line -
  • check continuity from the OB2 connector to the AS ECU connector.
  • Check 16 way harness connector is plugged in
  • Check 16 way connectors male/female for corrosion or broken wire (tug on each wire)
• Loss of power to the AS Unit -
  • check fuses.
  • Check earth eyelet tag connector on AS Unit, must be zero Ohms nominally.
• Faulty AS ECU - replace

Sorry responding by cell phone working from memory, no circuits to hand

 

@bronxteck @oceanbrave

Will do. Thanks for the help!

 

@JimmyNY
For communications essentially 2 things are required:-

1. The AS Module electronics is both functional and connected to +12V (BATT+) and OV, these being Pins 12 and 8 respectively.
   • Note the 16-Way carries no ground connection, instead AS Module Pin 8 connects directly to the AS Unit chassis which in-turn connects to the vehicle chassis, so this connection is VITAL. Disconnect the battery, Pin 12 should measure low resistance to positive lead and Pin 8 to the negative lead..
2. The Class2 Serial bus is connected to the BCU.
   • The OBD2 Data Link Connector Pin 2 (Below the Steering Column) connects to the 16-way connector C451 Pin 3 which ultimately connects to at Air Suspension Module Pin 10, these two points should measure low resistance between them.

The AS Electronics is powered at all times, so with both power and serial comms it should communicate with the Tech2, if not then the module itself could be faulty.

My experiences with Hummer electronics began with a faulty AS Module, after many long hours I managed to repair it and keep it as a spare. The module itself is "potted" in rubber and very difficult to extract putting it beyond economical repair.

Note also the Tech2 should be set for the correct model year which is not necessarily the same as purchase date.

 

Tried it on 3 different model years, unfortunately without luck. A connection to the AS cannot be established.

The car is at the mechanic at the beginning of March. I'll let him review all your suggestions

 

Seems likely there is a genuine loss of communications.

Also be careful to power the Tech2 ofrom the OB2 via the cable supplied, do not use a 12V power outlet.