3-second answer: Pull codes with a paperclip: jumper the STI pin to signal return on the OBD-I connector under the hood (passenger fender), turn the key on, and watch the CEL flash. KOEO codes flash first (twice = code 11 = pass), then a separator flash, then KOER codes (engine running). Long flash = tens digit, short = ones.
How to read the flashes
- Long flash = 10, short flash = 1. Code 23 = two longs, pause, three shorts.
- KOEO test (key on, engine off): codes appear twice, then a "separator" (a 1.5s flash), then the continuous-memory codes.
- Code 11 = system pass.
The common codes (92-96 EEC-IV)
| Code | Meaning |
|---|---|
| 11 | System pass |
| 12 | No RPM signal (during KOER) |
| 13 | No RPM signal (steady) |
| 14 | PIP circuit failure |
| 18 | SPOUT circuit open |
| 21 | ECT sensor out of range (coolant temp) |
| 22 | MAP/BP sensor out of range |
| 23 | ACT sensor out of range (air temp) |
| 24 | ACT sensor — high |
| 31 | PFE/EGR pressure sensor |
| 32 | EGR valve not closing |
| 33 | EGR valve not opening |
| 34 | EGR valve position (EVP) circuit |
| 41 | O2 sensor — lean (always lean) |
| 42 | O2 sensor — rich (always rich) |
| 44 | O2 sensor — lean (system) |
| 45 | O2 sensor — rich (system) |
| 51 | ECT sensor — open |
| 52 | PSOM/PSP sensor |
| 53 | TPS voltage high |
| 54 | ACT sensor — open |
| 63 | TPS voltage low |
| 67 | Clutch switch circuit |
| 72 | TPS fault (KOER) |
| 74 | Brake on/off (BOO) switch |
| 81 | Air management (smog) solenoid |
| 84 | EGR vacuum regulator |
The honest note
Codes point you to a circuit, not a part. A code 21 (ECT) is often a corroded connector or a thermostat problem, not a new sensor. And codes are only as good as the wiring — check grounds first. This is the #1 lesson from 30 years of OBS forum threads.
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