Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1990 Mercury Grand Marquis LSFACTORY OEM SERVICE PROCEDURE
KOEO Code/Test Menu - 5.0L
KOEO SELF-TEST - CKT TEST & STEP MENU
| Code No. | Go To: Test No. (Step No.) |
|---|---|
| 15 | QB (3) |
| 19 | QD (5) |
| 21 | DA (1) |
| 22 | DF (1) |
| 23 | DH (1) |
| 24 | DA (1) |
| 26 (MA PFI Only) | DC (1) |
| 31 | DN (1) |
| 32 | DN (25) |
| 34 | DN (20) |
| 35 | DN (5) |
| 51 | DA (10) |
| 53 | DH (3) |
| 54 | DA (10) |
| 56 (MA PFI Only) | DC (20) |
| 61 | DA (20) |
| 63 | DH (1O) |
| 64 | DA (20) |
| 66 (MA PFI Only) | DC (10) |
| 67 | FA (1) |
| 79 | FA (10) |
| 81 | KC (8) |
| 82 | KC (8) |
| 84 | DN (10) |
| 85 | KD (6) |
| 87 | J (7) |
| 95 | J (20) |
| 96 | J (30) |
| No Codes/Codes Not Listed | QA (1) |
Factory Service Tools
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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