Computer World

Planet Fox > Computer World > Inside of a Car Computer

Inside of a Car Computer

Pretty much all cars built in the last 40 or so years use a real time computer called an engine control module (ECM). The purpose of the ECM is to manage all of the engine's functions. On a carbureted engine, the carburetor will have dozens of solenoids and valves, which are controlled by the ECM, based on feedback from pressure, speed, and oxygen concentration sensors throughout the vehicle. The operation is similar on newer cars with fuel injection, but a little simpler: the fuel injectors have two states, on and off, and the fuel flow and metering is controlled directly by the ECM, which turns the fuel injectors on and off rapidly, varying the width of the pulse to change fuel concentration.

More advanced designs, such as the first one on this page, also have sensors in the powertrain of the vehicle. Vehicles equipped with electronic, multi-spark distribution, formerly known as an MSD ignition after the company that popularized it, also use the ECM to control spark timing. Through its various sensors the ECM can even determine what's wrong with a malfunctioning engine, while it's running it monitors performance data, whenever a parameter deviates too much from a preset maximum, it sets a flag which turns on the check engine light (MIL) and stores a standardized trouble code, which can be read by a device connected to its CAN bus. For example, the trouble code P0308 is a misfire in cylinder 8.

Here I've taken apart and photographed two engine control modules.

Pontiac Parisienne

This first one is from a 1984 Pontiac Parisienne (essentially the same thing as a Chevy Caprice). It had an electronically controlled Rochester QuadraJet 4 barrel carburetor, a gasoline powered V8, 305 CID engine with a "Turbo Hydra Matic 9000" automatic transmission. This module was hidden inside the plastic trim, under the dash on the passenger's side.

The first thing you'll notice is how shiny everything is, this is because the boards are dipped in lacquer to prevent dust and corrosopn from causing problems. All of these chips have proprietary "DELCO" part numbers, so I can't tell you with certainty which components do what, but we can probably guess a few things just from chip placement and what kind of things would be required. The 40 conductor card-edge connector on the left (J1) was used for interfacing to the vehicle wiring, the 40 pin card edge connector on the right (J4) wasn't connected to anything and was also covered in lacquer, so it's safe to assume this was for internal, factory testing or programming.

The power conditioning circuitry is at the top left and consists of an electrolytic capacitor, metal oxide varistor, a couple of ICs which are probably for voltage regulation, and a few resistors, ceramic capacitors, and diodes. The casing was bent over to double as a heatsink.

All of the chips are soldered to the board, except for the one at the top right (U13), which is socketed. This is most likely a mask ROM containing programming/firmware and data about the car. The chips on the far left, U15, U16, and U17, along with the other small chips on the board are most likely common logic gates. The larger 28 pin DIP chip at the bottom, U11, is probably an analog to digital converter.

The four 40 pin DIP chips at the bottom are likely either more A/D converters, signal processing, or proprietary interface logic. Since this was manufactured in 1983, it's highly likely that one of the 40 pin chips is a Zilog Z80 or compatible 8 bit CPU. Another would likely be SRAM, which could be used for working memory and storing trouble codes, since it retains its data for short periods when the power is removed. The crystal in the lower right corner is for generating a clock signal, and is marked 4.1931 MHz, which is a pretty standard clock rate for an early 80s computer.

While all of the components on the top of the board are through hole, the ones on the opposite side are surface mount.

High Resolution, Top (217 KB)
High Resolution, Bottom (157 KB)

Table of Visible ICs

Delco Part Number
U14, U20
U15, U16, U17

If you have information or datasheets for any of these ICs feel free to contact me. This one isn't being used for anything, and I think it would be cool to recycle some of the components into something else.

2000 Mercury Grand Marquis

This one is out of the car I drive every day, so I had to put it back once I was done taking pictures of it. It's hidden inside the passenger compartment under the dash against the firewall on the driver's side, and is connected to the wiring inside the engine compartment with a large 48 pin weatherproof pin and socket type connector.

You can still see that they're coating these in a heavy layer of lacquer. This looks to be less densely populated, even though it performs more functions than the one above. Newer chips tend to do more in less real-estate. Notice that the last one we looked at had almost exclusively through hole components, while this newer one is almost exclusively surface mount. These chips all have manufacturer part numbers, but they seem to be part numbers exclusive to the vehicle manufacturer since I can't find datasheets for any of them. However, you can still make some educated guesses.

The electrolytic capacitor and voltage regulator at the top right are the power supply circuit. Along the right side you will see 47 surface mount capacitors and resistors, one for each pin of the connector, minus the one used for + power. Some of these are decoupling capacitors, used to block DC while allowing AC and limit the amount of AC current. Others are resistors, which are used to limit AC and DC current.

One thing you'll notice right away is that almost all of the ICs are made by Motorola. The two SOIC chips on the far right are almost definitely line drivers or buffers, used to convert the incoming signals to logic level and vice versa. The two PLCC chips on the right are probably some type of specialty interface logic or application specific integrated circuits (ASIC), one of which I'm told is an ignition controller. The 160 pin QFP chip in the middle is almost definitely the CPU, which is likely to have at least the core of one of the Motorola 68k family of 32 bit processors, such as the 680x0 or the Cold Fire series. The clock oscillator is at the center and is rated 60 MHz.

The PLCC chip to the left of the CPU with an Intel label is an EEPROM used to store the firmware, programming, instructions, and data about the car. One of the other SOIC chips near the CPU would be another EEPROM used for storing performance data and trouble codes from the last x number of minutes. At the far left is a 30 pin card edge connector, which isn't connected to anything in the car. It would likely be used for factory testing, in-circuit programming of the EEPROM, and potential future changes to the EEPROM code.

Systems like this in general don't tend to have a lot of memory, since they're working with real time data. I don't see anything on the board that looks like RAM, but I didn't see the underside of the board since it's in there pretty tight and I didn't want to damage it, so it's probably on the other side.

High Resolution, Top (201 KB)

Table of Visible ICs

Chip Carrier
Part Number

If you have any information on the function of any of these chips or, better yet, datasheets, then please feel free to contact me.

Powered by FreeBSD
Valid HTML 4.01
Site Map
©MMIX-MMXIV Planet Fox