BK / GQ engine controller
Karen Abse said:
I got the car well used from an auction so I don't know if there are any modifications. How can I tell?
No bio-disiel.
I was low on fuel with a couple of gallons in the tank. It's running a little rough and when I scooted out into traffic, it missed some.
Thanks.
Karen
Your check engine light (CEL from now on) probably came on from the missfire. I suspect that the high output signal from the fuel injector pump during this acceleration attempt did not match the low engine rpm speed during this missfire and that this discrepancy created a notice of a fault. Air in the fuel lines will do this. The low fuel level may have contributed. Consider replacing the fuel filter and checking the integrity of the hose ends and the seal of the thermal valve on top of the filter.
The 1996 Passat came from the factory with an engine control unit (ECU, another acronym to remember). There was an updated version for the 96 ECU introduced during the 97 model year run. These two 96 ECUs are identified by the suffix after the part number. The original 96 ECU has a BK suffix. The newer 96 ECU has a GQ suffix. Knowing which ECU you have will assist in determining which modifications are benefitial and should be considered, and which are unnecessary or even detrimental.
The ECU is mounted under the hood in the area near the right windshield wiper. Lift up the black splash shield covering the cabin air filter and look under. The original BK is in a black plastic case, was built before compliance with the second generation of the industry standard On Board Diagnostics (OBD II) was required, but supports some diagnostics (under the prior OBD protocol) without additional code readers. The GQ is in a silver color cast metal case, is OBD II compliant and requires a code reader for all fault codes.
If the ECU in your Passat is a black plastic case BK version, a code can be read from the check engine light by following these steps:
1, Turn the ignition key to ON, but not to the START position.
2, Quickly press the accelerator pedal to the floor and quickly release it five times within five seconds.
3, Wait about 5 seconds.
A BK series ECU will begin to flash the yellow lamp in a four digit sequence. Counting the number of flashes will produce a code from 1111 to 4444. This code can be looked up in a table to determine the fault. A GQ series ECU will not flash the yellow lamp. This GQ ECU requires an OBD II reader for all faults.