Code
C90A
CITROEN
C — Chassis
Reception quality fault: Open circuit
AI status
Completed
Completed
100%
Causes
- Broken or disconnected antenna coax or wiring
- Corroded or loose antenna connector
- Faulty antenna (broken element or mast)
- Failed antenna amplifier (power or internal open)
- Blown fuse or loss of power/ground to antenna amplifier or head unit
- Damaged or shorted connector pins in harness or head unit
Symptoms
- Weak or no radio reception (FM/AM/DAB) or poor signal quality
- Audio system reports a reception or antenna error message
- Intermittent reception that improves with movement of wiring/connector
- No handsfree or telematics reception if antenna is shared
- Related modules show additional communication or antenna faults
What to check
- Scan vehicle for codes and note any related or accompanying DTCs
- Visual inspection of antenna, mast, base, coax routing and connectors for damage or corrosion
- Check fuses and relay(s) supplying the radio/antenna amplifier
- Inspect and tug connectors to check for loose contacts
- Measure continuity of coax from antenna mast to head unit (or amplifier) with multimeter
- Measure supply voltage and ground at antenna amplifier/power feed with ignition on
Signal parameters
- Antenna coax continuity: low resistance (near 0 ohms short-circuit to the center conductor is not expected; check shield and center conductor continuity separately)
- Typical coax characteristic impedance: vehicle systems commonly use ~50–75 ohms (verify with manufacturer)
- Antenna amplifier supply: approx. battery voltage (~11–14 V) with ignition/accessory on (verify exact value per model)
- Antenna amplifier control signal: check CAN or dedicated control line presence if applicable
- Expected head unit antenna input: presence of received RF signal and variable level depending on environment (use diagnostic tool or RF tester)
Diagnostic algorithm
- Read and record C90A and any other stored codes. Note freeze-frame or live data related to reception if available.
- Perform a visual inspection of the roof antenna/mast, base, and wiring harness for obvious damage, corrosion, or water ingress.
- Verify fuses and power/ground to the head unit and antenna amplifier. Replace any blown fuses and re-test.
- Disconnect the antenna connector at the head unit (or amplifier) and inspect pins for corrosion or bent pins. Reconnect and wiggle test while observing for changes.
- Measure continuity of the center conductor and shield from the antenna mast to the head unit input. An open reading indicates a broken coax or connector.
- Measure supply voltage at the antenna amplifier power feed with ignition on. No voltage suggests wiring/fuse/relay problem upstream.
- If the antenna amplifier is removable/testable, bench-test or substitute with a known-good unit. If amplifier is integral to the head unit, consider head unit bench testing or replacement.
- If wiring and amplifier check good, check module software/version and reflash or update if a known fix exists for reception faults.
- After repairs, clear DTCs and road-test to confirm reception restored and code does not return.
- If problem persists after component/harness replacement, escalate to manufacturer technical support for module-level diagnostics.
Likely causes
- Open / disconnected antenna coax or connector
- Failed antenna amplifier (open output or no power)
- Blown fuse or missing power/ground to amplifier/head unit
- Damaged antenna (physical break or corrosion at base)
Fault status
Status
Open circuit detected on reception/antenna input. The antenna feed or amplifier is not providing a usable signal; inspect antenna, cabling, connectors, power and ground.
Repair difficulty: Medium
Diagnostic time: 1.0 - 2.5 hours
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