Code
P1641
SATURN
P — Powertrain
FC Relay 1 Control Circuit
AI status
Completed
Completed
100%
Causes
- Blown fuse related to relay circuit
- Faulty FC Relay 1 (stuck or coil open)
- Open, shorted, or corroded wiring or connector in relay control circuit
- Poor ground at relay or PCM ground point
- Intermittent connection (water intrusion, broken wire)
- PCM output driver fault or internal PCM damage
Symptoms
- Check Engine Light (MIL) illuminated
- Relay clicking unusually or not clicking when expected
- Related system inoperative (dependent on relay function)
- Intermittent operation of components controlled by the relay
- Possible no-start, no-crank, or loss of a function if relay supplies critical system
What to check
- Retrieve and record freeze frame and stored DTCs with a scan tool
- Check battery voltage (should be 12.4–12.8 V at rest)
- Inspect related fuses and fusible links visually and with a meter
- Visually inspect relay, relay socket, and wiring harness for damage, corrosion, pin push-out, or water entry
- Backprobing: measure voltage at relay control terminal with key ON/engine cranking
- Check continuity and resistance of control wire from PCM to relay socket
Signal parameters
- Relay control voltage: 0 V (inactive) to battery voltage (~12 V) when PCM commands ON (or ground-switched depending on design)
- Expected coil continuity: typically 50–200 ohms (varies by relay)
- Open-circuit: infinite resistance at coil terminals
- PCM driver output: switches to ground or battery voltage (verify with backprobe)
- No-load current draw through relay coil: small (tens to hundreds mA)
Diagnostic algorithm
- Use a scan tool to confirm P1641 and note freeze frame and related codes. Do not assume cause without testing.
- Verify battery voltage and charge if weak. Repeat code check after ensuring solid supply.
- Inspect fuses and fusible links for the relay circuit; replace if blown and investigate cause.
- Visually inspect the relay, socket, and harness for corrosion, bent pins, or water intrusion. Repair or replace damaged connectors.
- With ignition ON, backprobe the relay control terminal: if PCM should drive high, verify battery voltage; if PCM should pull to ground, verify near 0 V when active. Compare with expected behavior from service data.
- Check coil resistance across the relay coil terminals. If open or out of spec, replace relay.
- Perform continuity/short checks between relay control terminal and PCM terminal. Repair wiring faults: splices, chafes, shorts to ground or battery.
- Verify relay ground(s) and PCM ground connections for low resistance to chassis. Clean and tighten grounds as needed.
- If wiring and relay check good, command the relay on/off with a scan tool while monitoring control voltage. If PCM does not command or shows incorrect output, suspect PCM driver — consult manufacturer repair information before replacing PCM.
- Clear codes and perform a functional test/road test to confirm repair and that code does not return.
Likely causes
- Faulty or stuck FC Relay 1
- Corroded/loose relay socket or connector pins
- Open/shorted relay control wire between PCM and relay
- Blown fuse feeding the relay or PCM power feed
- PCM driver transistor failed
Fault status
Status
PCM detected an abnormal condition (open, short, incorrect voltage, or no response) in the control circuit for FC Relay 1. This indicates an electrical fault in the relay control circuit that requires inspection of fuses, relay, wiring/connectors, grounds, and PCM output.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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