How to Check Prelude 3rd Gen ECU Error Code

On '88-'91 Preludes the ECU is located under the carpet on the right passenger floorboard. There will be a small flap in the carpet you pull up to see the ECU LED.

Dont forget, if your throwing a code use the ONLINE MANUAL to isolate and fix the problem.

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But wait a minute, how do I know if my car is OBD0 or OBD1?!!!!

All 88-89 are OBD0.
90-91 that came with a B20a5 are OBD0 too. (These were the "2.0SI" models in the U.S.)
90-91 that ORIGINALLY came with a B21a1 are OBD1.(The "SI" models in the U.S.)

Wait a sec, what if someone swapped motors before I got the car huh?!

An easy visual check is this: Look at the exhaust manifold on the front of your motor, near to the bottom of it you will see 2 O2 sensors screwed into it if your car is OBD0. If you DON'T see any o2 sensors there then your car is OBD1. (OBD1 cars have a single o2 installed in the downpipe under the motor.)

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The codes:

'88-'91 PGM-FI (OBD0)

Code 0 ECU
Code 1 Oxygen content A
Code 2 Oxygen content B
Code 3 MAP sensor
Code 4 Crank angle sensor
Code 5 MAP sensor
Code 6 Coolant temperature
Code 7 TPS sensor
Code 8 TDC position sensor
Code 9 No.1 cylinder position sensor / CYL sensor
Code 10 Intake air temperature sensor
Code 11
Code 12 Exhaust gas recirculation system
Code 13 Atmospheric pressure sensor
Code 14 Electronic idle control
Code 15 Ignition output signal
Code 16 Fuel injector
Code 17 Vehicle speed sensor

'90-'91 PGM-FI (OBD1)

Code 0 ECU
Code 1 Oxygen content A *, Oxygen content **
Code 2 Oxygen Content B
Code 3 MAP sensor
Code 4 Crank angle sensor
Code 5 MAP sensor
Code 6 Coolant temperature
Code 7 Throttle position sensor
Code 8 TDC position sensor
Code 9 No.1 cylinder position sensor / CYL sensor
Code 10 Intake air temperature sensor
Code 11
Code 12 Exhaust gas recirculation system
Code 13 Atmospheric pressure sensor
Code 14 Electronic air control
Code 15 Ignition output signal
Code 16 Fuel injector
Code 17 Vehicle speed sensor
Code 41 ** Oxygen sensor heater
Code 43 ** Fuel supply system
* 2.0 liter engines
** 2.1 liter engines
Clearing ECU codes
Stored codes are earased from memory by disconnecting power to the ECU for at least 30 seconds. Disconnecting the negative battery cable will clear the memory of the ECU, as well as other solid-state equipment such as radios. The ECU may also be cleared by pulling the appropriate fuse from the underhood fuse and relay box. This may be the BACK-UP, CLOCK or CLOCK/RADIO fuse.



'88-'90 PGM-CARB

Code 1 Oxygen content
Code 2 Vehicle speed pulser
Code 3 MAP sensor, electrical signal
Code 4 Vacuum switch signal
Code 5 MAP sensor, vacuum signal
Code 6 Coolant temperature
Code 7 Clutch switch signal (manual trans.)
Code 7 Shift position signal (auto trans.)
Code 8 Ignition coil signal
Code 9 Intake air temperature
Code 10 Electronic Air Control Valve (EACV)