Why is this odd game played with car purchases? I think the persistence of the let’s-make-a-deal approach is a result of high prices and the fact that most people mistakenly think they’re savvy negotiators.

Recently, I took the plunge and bought a new Chevy van. I put up an admirable fight (hint: bring your own bad guy, aka, your wife), but sincerely doubt the dealer lost money on the deal. Anyway, purchasing the new van is the reason I’m suddenly on this car computing kick. As you’ll see, the collision of modern technology and the somewhat bizarre ways of the car business makes a trip under the hood of a modern car worthwhile.

HOOKING UP

Testimony to the fact that times have changed, when I ordered shop manuals for the van, I discovered almost 600 pages devoted to the subject of engine controls versus a mere 200 for engine mechanical.

Interest piqued, I poked around under the dash and found, as you will on any ’96 or later vehicle, the Data Link Connector (DLC) shown in Figure 1, which serves as a gateway into the vehicle’s LAN.

Note that out of the 16 pins, only the power, ground, and data line(s) (whether J1850, ISO, or CAN) are strictly specified (in SAE J1962). In GM vehicles, the single-wire version of J1850 uses pin 2. The rest of the pins are available for proprietary use by each manufacturer.

When you take your car for service, a scan tool gets plugged into the DLC. As you’ll see, this allows the repair technician to quickly and easily get a good picture of what is, and what has been, going on under the hood.

Perusing the shop manuals further, I found that my van incorporates all manner of electronic sensors and sub-systems that operate under the watchful direction of the Vehicle Control Module (VCM, see Photo 1).

According to the specs I found at Delphi (the spinout of formerly captive GM parts-supplier, Delco), my VCM incorporates a 16.7-MHz 32-bit microcontroller (MC68332), a healthy half-megabyte of flash memory, and 6 KB of RAM.

With 160 I/O connections, the to-do list for the VCM is certainly full. Practically on a rev-by-rev basis (i.e., hundreds of hertz), the VCM deals with the myriad of sensors and actuators responsible for low-level control of the powertrain—spark timing, fuel/air mixture, transmission shift points, and so on. Furthermore, the VCM continuously runs reality checks to detect component failures and compensate as best it can (i.e., limp home).

On a higher plane, the VCM coordinates activity across the powertrain as a whole, notably getting the engine, transmission, and brakes to work as a team. For example, as you travel over hill and dale, the VCM will update transmission shift characteristics depending on the circumstances, such as whether you’re towing a trailer at the time.

MIL SPEC

One fine morning I started the new van and left it idling while I ran back in the house. Upon jumping back behind the wheel, the "Service Engine Soon" message was glaring at me from the infamous malfunction indicator lamp.

With only about 500 miles on the clock, I wasn’t exactly a happy camper. According to the owners manual, driving the vehicle with the MIL on could lead to costly repairs that may not be covered by my warranty.

That’s just perfect. Though the van seemed to be running fine, the ominous wording left little choice but to make a trip to the dealer.

Fortunately, it turned out to be a false alarm. The repair technician hooked up a scan tool to the DLC and extracted Diagnostic Trouble Code (DTC) P0141, meaning the VCM felt that one of the oxygen sensors wasn’t heating up properly. I don’t know if the technician performed the intricate diagnosis of the oxygen sensor called for in the manual or just cleared the DTC (extinguishing the MIL), but the problem hasn’t popped up since.

Nevertheless, the episode prompted me to investigate further. Not to impugn anyone’s integrity, but forewarned is forearmed. When I go in for repairs, I like to be clued in and prepared to some extent.

I started cruising the Internet and found myself immersed in the regulatory depths of the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB). It turns out that one of the VCM’s most important roles is that of smog buster (i.e., continuously monitoring and tweaking operation to minimize air pollution). If the VCM thinks something isn’t kosher, it turns on the MIL.

Of course, everyone supports clean air, but be assured the advocacy is not all altruism on the part of car manufacturers. EPA and CARB may walk softly, but they carry a big stick.

In September ’98, for example, CARB ordered the recall of 330,000 Toyota and Lexus cars to replace onboard computers that failed to detect gas vapor leaks under normal driving conditions. At a cool $250 each, that adds up to more than $80 million. Rather a strong incentive to get it right next time.

Indeed, vapor leaks are considered a major pollution no-no, so modern vehicles have sophisticated EVAP (evaporative) systems that recycle fuel vapors. It’s up to the onboard computer to ensure that the fuel system doesn’t leak, and that’s why something so simple as not tightening the gas cap can turn on the MIL.

Another suspect to watch out for is misfire, incomplete combustion that not only pumps raw gas out the tailpipe, but can damage the catalytic converter. The VCM goes to great effort to detect misfire by statistically sampling variations in crankshaft speed and using camshaft position to isolate the problem to a single cylinder. To complicate matters, something as common as bouncing over a pothole can feedback through the drivetrain and mimic misfire. So, in the most advanced implementations, misfire detection is qualified by a "rough road" input from the brake or suspension module.

Even when all is well, a lot of pollution occurs in the first few minutes after a cold start. The challenge for the VCM is to achieve reliable starts and smooth idling without just throwing extra gas at the problem (as with yesteryears’ choke).

That’s why oxygen sensors have heaters. They need to be up to proper operating temperature before the VCM can enter the closed loop mode that continuously varies the fuel/air mix to achieve maximum performance and fuel economy with minimum smog.

OH BOY, DATA

Thanks to the regulatory might of the EPA and CARB, the name of the game when it comes to onboard computing is OBD II, the second-generation on-board diagnostics mandated by law since model year ’96.

While wandering around on the Internet, I perceived what appeared to be a tug-of-war between the various players who have high stakes on the table. The car companies seem biased toward keeping the inner workings a deep, dark secret. Meanwhile, the aftermarket repair shops are alarmed at the prospect of cars that can only be fixed by an authorized dealer.

Striking a balance between the two are the regulators. They want the procedures and tools needed to fix a smoker widely accessible, yet understand it’s not reasonable to expect manufacturers to disclose all. For example, the VCM not only controls the engine, transmission, and such, but also plays a role in theft prevention (e.g., disables starter in absence of a valid key signal).

Frankly, none of them seem too eager to let the lowly consumer have a clue. In particular, the regulators look askance at the emergence of power chips and such, going so far as to demand sophisticated countermeasures to prevent homebrew hot-rodding (i.e., reprogramming) of VCMs.

OBD II is the compromise solution. It openly standardizes (in SAE J1979) access via the DLC to the real-time (RPM, temp, vacuum, etc.) and historic freeze-frame information deemed necessary to correct emissions-related problems. It also defines the mechanism for retrieving and clearing DTCs (i.e., find out why the MIL went on and turn it off).

SCAN MAN

With the emergence of standards, as a trip to your local auto parts store will confirm, the average shade tree mechanic now has access to scan tools that were formerly the domain of dealers only. These are typically hand-held units that cost $200 or so, and get by with a keypad and small LED display or LCD screen.

There are also PC-based solutions on the market that offer pretty screens, hard-disk data logging, printed reports, and so on (see Photo 2). Generally, they use a converter dongle that connects the J1850 DLC to the PC’s serial port. Because the price is about the same as the hand-held units, these are likely to have more appeal for computer literate types. I discovered some interesting units available from Baum Tools, B&B Electronics, and Ease Simulations.

Whether hand-held or PC-based, these units are generally intended for hood-up inspection, maintenance, and repair. Indeed, as one supplier’s documentation notes, there’s no easier way to end up in a ditch than trying to drive while you’re fiddling around with one of these gadgets.

I was intrigued by the possible on-the-road applications. All I needed was a simple J1850-to-RS-232 adapter with enough brain power to get online.

Fortunately, I stumbled across an outfit called Multiplex Engineering, which offers such a gadget for less than $100 (see Photo 3). It was time to try my hand at a little high-horsepower hacking.

Photo 3—The Multiplex Engineering mux interface acts as a gateway between the vehicle network and anything with an RS-232 serial port.

PROGRAM J1850Tach
INTEGER rpm,i,j
INTEGER response(14)
STRING rpm_str
CONST leds=~$c038~
BEGIN
/* Mux interface msg to request RPM */
DATA $20,2,5,$68,$6a,$f1,1,$c,0,0,0,0,0,0,$d7
OUT 0,$74 /* '180 ASCI0 19.2K 8N1 */
OUT 2,$20
OUT 4,0
FOR i=0 TO 7 
OUT leds+i,ASC(" ")
NEXT i
OUT leds,ASC("R")
OUT leds+1,ASC("p")
OUT leds+2,ASC("m")
loop:
/* Send request RPM msg */
FOR i=1 TO 15
READ j
DO
UNTIL BAND(INP(4),2)<>0
OUT 6,j
NEXT i
/* Receive RPM response msg */
FOR i=1 TO 14
DO
UNTIL BAND(INP(4),$80)<>0
response(i)=INP(8)
NEXT i
/* Throw away mystery msgs */
IF response(3)<>$48 THEN GOTO loop
/* Convert RPM to 3 or 4 digit string, display on LEDs */
rpm = ((response(8)*256)+response(9))/4
rpm_str = STR$(rpm)
IF LEN(rpm_str)=10 THEN rpm_str=MID$(rpm_str,1,4)
ELSE rpm_str=CONCAT$(" ",MID$(rpm_str,1,3))
FOR i=0 TO 3
OUT leds+4+i,ASC(MID$(rpm_str,i+1,1))
NEXT i
WAIT 6 /* Spec requires 100ms min between msgs */
GOTO loop

40 82 48 6B 10 41 0C 0A E0 23 00 00 00 9F 
40 82 48 6B 10 41 0C 0A D9 9C 00 00 00 11 
40 82 48 6B 10 41 0C 0A FE 48 00 00 00 E2 

40 82 A8 FF 29 03 F0 00 00 00 00 00 00 45 

40 82 48 6B 10 41 0C 0A DC F5 00 00 00 6D 
40 82 48 6B 10 41 0C 0A E6 6D 00 00 00 EF 
40 82 48 6B 10 41 0C 0A EE 85 00 00 00 0F 
40 82 48 6B 10 41 0C 0A F3 C9 00 00 00 58 

40 82 E8 FF 10 03 B3 00 00 00 00 00 00 2F 

40 82 48 6B 10 41 0C 0A F9 1B 00 00 00 B0 
40 82 48 6B 10 41 0C 0A F4 9A 00 00 00 2A 
40 82 48 6B 10 41 0C 0A E9 D6 00 00 00 5B