Code
P1650
SCION
P — Powertrain
Cooling fan control relay malfunction
Views:
UK: 7
EN: 5
RU: 2
AI status
Completed
Completed
100%
Causes
- Failed cooling fan control relay (stuck contacts or coil open)
- Blown fuse for cooling fan circuit
- Open, shorted or damaged wiring in relay control or power circuits
- Corroded or loose relay or fan connectors
- Faulty cooling fan motor drawing excessive current or intermittent
- Poor chassis or engine ground for fan/relay circuit
Symptoms
- Cooling fan(s) fail to run when engine is hot or A/C is on
- Cooling fan(s) run continuously (relay stuck closed)
- Engine temperature rising or overheating at idle/stop-and-go
- Reduced air-conditioning performance in traffic
- Blown fuse or repeated fuse failures
- Check Engine Light / MIL illuminated with P1650 stored
What to check
- Retrieve stored freeze-frame and freeze data with scan tool; note conditions when code set
- Visual inspection of relay, fuses, wiring harness and connectors for damage, corrosion or disconnection
- Inspect and verify good battery and chassis/engine grounds
- Locate cooling fan relay and compare part number to OEM specification
- Check fuse(s) for fan circuit continuity and signs of intermittent failure
- With ignition ON, verify relay coil supply (12V) at relay power terminal
Signal parameters
- Relay coil supply (constant feed) ≈ 12V with ignition ON
- ECM control signal typically switches coil ground to activate (control terminal: ~0V when energized; ≈12V or open when de-energized) — confirm vehicle wiring polarity
- Fan motor supply when relay closed: ≈12V at fan connector
- Typical cooling-fan current draw (vehicle-dependent): single-speed ~8–20 A; dual-speed high stage higher — compare to OEM spec
- No-voltage/short to ground on control circuit when relay not commanded; no high resistance in coil circuit
Diagnostic algorithm
- Read and record freeze-frame and all stored U-codes; clear codes and attempt to re-create.
- Perform a visual inspection of relay, fuse, fan connectors and wiring for damage, corrosion or loose pins.
- Verify battery voltage and main power/ground integrity for fan circuit.
- Check fuses for continuity; replace if blown and retest. If fuse blows repeatedly, stop and trace short.
- With ignition ON, probe relay coil terminals: confirm constant 12V feed and ECM control terminal behavior when fan is commanded ON via scan tool (control should change state).
- Command fan ON using a scan tool and listen/feel for relay activation and fan motor operation. If relay clicks but fan doesn’t run, bench-test fan by applying 12V directly; measure current draw.
- If relay does not click when commanded but control output from ECM is present/expected, replace relay and retest.
- If relay clicks and control appears correct but fan operation abnormal, inspect wiring between relay and fan for opens/shorts and repair as needed.
- If wiring and relay test good but ECM control output is absent or inconsistent, verify ECM power/ground and consider ECM driver fault — consult OEM service info before replacement.
- After repairs, clear codes and road/test to confirm the fault does not return.
Likely causes
- Faulty cooling fan relay (most common)
- Damaged wiring or connector at relay/fan
- Blown fuse or poor ground
- Fan motor short or seizure causing relay to trip or fail
- Rare: ECM driver fault
Fault status
Status
ECM detected abnormal behaviour in cooling-fan relay control circuit (relay did not respond or control signal out of spec). Inspect relay, fuse, wiring, fan motor, and ECM outputs.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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