GM Tech 2: How your Saab talks to your mechanic
January 25, 2008 in Archive
Tedjs, our resident tech guy, has kindly provided this insight into the modern mechanic’s Swiss Army Knife – GM’s Tech 2 (or Tech II as you’d write it if search engines didn’t exist.)
I’d like to thank Ted for taking the time and giving us this insight into the little electronic doodads that control our Saab vehicles. Hopefully this will be the first of a few articles on this.
Enjoy the journey….
If you really want to know what your Saab is thinking about when you’re motoring around town this holiday season, hopefully Santa will have dropped the following pieces of hardware off for you:
- A GM Tech II scan tool
A CANdi module so the Tech II can talk to the high speed network on your Saab
And of course the Saab software program for the Tech II
GM kindly supplies our school with all this hardware. All I needed was my Saab to give the Tech II something to do. My 2007 9-3 Aero has the turbocharged V6 and six speed automatic, so that is what will be referenced here.
A little background before we dig in….
Here in the United States all vehicles communicate via a standardized or OBD II style data link connector, so if you crawl under the dash of your 1996 and up Saab you should find the connector. This is where the scan tool plugs in and becomes part of the data network.
This connector allows any OBD II compatible scan tool to ‘talk’ to the vehicle. Those of you who live in the USA that do state mandated emission testing may find that they now just plug into your vehicle for verification of the vehicles emission compliance.
Ultimately, all of powertrain components such as the engine and electronically shifted transaxle terminate on pins 6 and 14 of the DLC on what is a high speed or Controller Area Network (CAN). The CAN network is a standard high speed communication protocol that is used on most vehicles sold in USA and allows devices ‘on the data bus’ to communicate at speeds of 500 kilobits per second. This becomes critical when transmission and engine control modules must chat with each other to control the powertrain.
One thing we did not have with the original Tech II package was the pictured CANdi module. With the advent of higher speed data networks, Tech II needed an additional piece of hardware to talk to modern vehicles which is the CANdi or Controller Area Network Diagnostic Interface. The ‘interface’ essentially digests all the information that is sent from the vehicle and sends it to the Tech II in manageable pieces so the scan tool can process the information.
Tech II itself has been around since 1996 and in my opinion is one of the best scan tools on the market for a GM vehicle. Some manufactures have gone to PC based tools and although these are cheaper from a hardware standpoint (you buy the PC) – they are simply not very ergonomic if you are driving around with one on a daily basis.
Tech II software for Saab is loaded onto a 32MB via GM’s Techline Information System or TIS software.
GM’s TIS application is now available via the web, which means no more software disc’s to distribute to dealers, which is nice. The technician needs only to select and load the software onto the Tech II.
It is possible to load a number of applications on the Tech II depending on what you need the tool to do. The North American application covers all domestic vehicles and of course – Saab automobile covers current Saab 9-3 and 9-5 vehicles.
After selecting options – diagnostic software is loaded onto the tool.
Once Saab software is finally loaded -the user is presented with the Saab Tech II splash screen
The heart of Saabs 2.8L V6 is a Bosch ME9 engine management system. The ME9 ECM regulates engine torque by controlling intake air charge, fuel and ignition timing. Once programmed to the vehicle – the technician can ‘see’ all sorts of data that might provide information that would help them troubleshoot and repair a vehicle.
Below is an Engine Control data list with key on, engine off.
One might be looking at this information to determine if engine coolant temperature (ECT) is reading properly at maybe a cold start. The temperature sensor measures the engine temperature and the ECM uses the reading to deliver more fuel to the engine when the engine is cold, control the cooling fans and perform OBD II diagnosis among other things. Thermostat diagnosis is performed by the sensor to ensure the engine is reaching proper temperature within a predetermined time frame.
ME9 uses a ‘drive by wire’ setup so when the driver depresses the accelerator pedal a ‘throttle request’ is sent to the ECM. ME9 can now decide how much torque to deliver to the wheels and open the throttle, increase turbo boost and modify fuel and spark to accommodate demands of the driver. A technician may be viewing this data to check and see if the requested boost is available to the engine.
The charge air pressure sensor (shown below right) is the sensor that is used to monitor this information. Air leaks on some Saab vehicles are presented to a technician as ‘air mass deviation from calculated’.
Tech II also has the ability to do some output tests on the vehicle. One test I have not seen on other vehicles is a compression test on the scan tool. A compression test is generally done to check if a cylinder is sealing. The Tech II can initiate what is essentially a relative compression test. The crankshaft position sensor is used to ‘look’ for fluctuations in crankshaft speed and readings are given to the technician.
The Tech II is needed for much more than powertrain controls. Screens shown below show the scan tool communicating with the active handling system on the vehicle. The electronic stability program ‘communicates’ with ME9 via the high speed network and might tell the engine controller to reduce torque if it decides that is the best strategy to get your Saab pointed back in the right direction.
Aligning your Saab at home (hope not!) or taking it in to get it going straight again? Hopefully the technician knows that the stability program needs to be recalibrated so that it ‘knows’ the car has been aligned and the wheels are pointing straight ahead. Once alignment adjustments are made, Tech II can tell the module that the wheels are pointing straight ahead.
Well, that’s all for now. In addition to having a lot of fun driving my Saab, I am learning more about all the technology that rides around with the vehicle. I will be assembling information over my next teaching semester as there is a lot of technical information the vehicle that I can use in my presentations. I will pass on to Swade periodically as time permits.
Questions are welcome.