| Symptom | Likely Pin/ Circuit | | :--- | :--- | | No start, fuel pump doesn’t run | A16 (fuel pump), B11 (starter signal), EFI relay (A2) | | No start, no spark | C1 (IGT), B13 (IGF), distributor ground | | Rough idle, stalls | A6-A9 (ISC valve), B14 (IDL contact), B10 (MAP) | | Poor fuel economy | B16 (O2 sensor), B22 (VF1) | | ECU resets every time | B19 (Backup power) | | Transmission shifting issues (auto) | B9 (Park/Neutral position) |

Let’s put this to work with real diagnostic scenarios.

: Ignition Timing signal sent from the ECU to the igniter to trigger a spark.

Pin numbering is usually read Left to Right, Top to Bottom.

Reference: Toyota Technical Information System (TIS), 4A-FE Engine Control Manual (Pub. No. RM201E), and field testing.