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Toyota 5S-FE engine factory workshop and repair manual download

Goal: diagnose, test and replace a failed relay on a Toyota 5S‑FE (EFI/fuel pump/other electrical relay). Below is an ordered, theory‑based procedure with clear test criteria and explanation of how replacing the relay fixes the fault.

1) Identify the relay
- Locate the correct relay in the engine-bay/junction/fuse box or under the dash (relay layout is printed on the lid). Common engine‑related relays on 5S‑FE cars: EFI/Main relay, fuel‑pump relay, fan relay, starter relay. Work only on the one that corresponds to the symptom (no start/fuel pump/noise = fuel pump or EFI relay).

2) Quick symptom check (what the relay controls and what failure looks like)
- Relay open (coil open or contacts open): controlled load (fuel pump, injectors, fan) gets no power → engine won’t start, pump silent, fan won’t run.
- Contacts stuck open/oxidized/high resistance: partial voltage to load → rough running, stalling, weak pump flow.
- Contacts welded or stuck closed: load runs continuously.
- Intermittent relay: intermittent stalling or no-start due to intermittent contact or intermittent coil activation.

3) Theory of operation (how the relay functions)
- A relay is an electromechanical switch: a low-power control circuit energizes a coil, creating magnetic force that moves a metal armature to close (or open) a high‑current contact circuit.
- In cars: coil side is driven by ignition switch or ECU; contact side connects battery power (usually fused) to the load. The relay provides isolation and allows small control circuits to switch large currents safely.
- Failure modes: coil open (no magnetic force), coil short (draws too much current), weak spring/dirty contacts (poor contact pressure), pitted/oxidized contacts (high contact resistance), broken solder/wiring in the relay block.

4) Safety and tools
- Tools: multimeter, jumper wires or bench 12 V supply, small screwdriver to remove fuse box lid, replacement relay (OEM or equivalent rated), optional test light.
- Safety: work with ignition off for removal. If testing a live circuit back‑probing, be careful, wear eye protection. If disconnecting battery, note radio/ECU memory.

5) On-vehicle diagnosis, ordered tests (fast and low-risk)
A. Visual / audible:
- With ignition ON, listen for a click from the relay when it should energize (e.g., key ON for fuel pump).
- Inspect socket and relay for corrosion, melted plastic, loose fit.
B. Swap test (fastest practical check):
- If another identical relay is present (same part number), swap them. If the fault moves with relay, relay is bad.
C. Voltage/coil check:
- With ignition ON, measure between the two coil terminals in the socket: you should see battery voltage (or the ECU control voltage) on one terminal and ground on the other when the relay is commanded. If coil control voltage is absent, the problem is upstream (ignition switch/ECU/fuse/wiring).
D. Functional output check:
- Back‑probe the relay’s switched output terminal in the socket. With the relay energized, the switched terminal should be battery voltage (within ~0.5 V). If coil energizes (click or control voltage present) but switched terminal is low or fluctuating, the relay contacts are bad or there is a wiring/fuse problem on the output side.
E. Coil resistance (bench or in‑place with relay removed):
- Typical automotive relay coil resistance ~50–300 Ω (varies by relay). Measure coil terminals on the removed relay: an open (infinite) indicates bad coil; a short near 0 Ω indicates a shorted coil. Compare to spec if available.

6) Bench test (confirms relay internals)
- Remove relay. Apply 12 V to coil terminals; you should hear a distinct click. Measure continuity between common and normally open (NO) contact: closed when coil is energized, open when not. Contact resistance when closed should be very low (<0.5 Ω ideally; low single ohms at worst). High contact resistance = burned/oxidized contacts → replace.

7) Replace relay (ordered steps)
- Obtain correct replacement relay (same pinout and current rating).
- Turn ignition OFF. Remove faulty relay from socket (pull straight out).
- Inspect socket and wires for heat damage; if socket is bad, replace or repair connector.
- Insert new relay firmly into socket.
- Start car or perform the relevant activation and recheck functions (fuel pump priming with key ON, engine starting, fans running).

8) Confirm repair and related checks
- Confirm load sees full battery voltage when relay energized (no voltage drop).
- If original fault was intermittent, verify consistent operation through warm/cool cycles and some idle/run time.
- If relay replacement did not fix symptom, measure voltage at the load itself (fuel pump motor/fans) to isolate wiring or load failure.

9) Why replacing the relay fixes the fault (concise theory)
- The relay contains the coil and the switching contacts that provide battery power to the load. If the coil is open, it cannot actuate the contacts, so no power reaches the load—replacing the relay restores the electromagnetic actuation.
- If the contacts inside the relay are pitted/oxidized or welded, they present high resistance or fail to open/close correctly. A new relay restores a low‑resistance metal‑to‑metal contact path so the load receives full voltage/current.
- If the relay socket wires were loose/corroded and the relay sat poorly, fitting a new relay can also restore proper contact pressure and conductivity (but if the socket is damaged you must repair the socket too).

10) Measurement targets / acceptance criteria
- Coil continuity: finite ohms (spec varies), not open or short.
- Audible click when 12 V applied to coil.
- Switched terminal voltage when energized: within ~0.5 V of battery.
- Contact resistance closed: very low (<<1 Ω).
- Symptom resolved: pump runs/engine starts/loads operate reliably.

Done.
rteeqp73

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