Code
DF992
RENAULT
D
-> P1644 - relay control heater 1
AI status
Completed
Completed
100%
Causes
- Faulty heater relay (coil or contacts)
- Blown fuse for heater/relay circuit
- Open or shorted wiring between ECU and relay
- Corroded/loose relay connector or ground
- Failed heater elements (overload or short)
- Faulty ECU driver or internal ECU fault
Symptoms
- Glow/heater warning light illuminated or service message
- Difficult cold starting or extended cranking time (diesel engines)
- Reduced engine performance or limp mode in some cases
- DTC stored (P1644) and related symptoms repeatable when heater relay should operate
- Possible repeated clicking or no clicking from relay when key is cycled
What to check
- Read all stored codes and freeze-frame data with a diagnostic scanner; note related codes and battery voltage at time of fault.
- Visually inspect relay, fuse(s) and relay socket for corrosion, heat damage or loose terminals.
- Check battery voltage (should be ~11–15 V) and engine ground integrity before tests.
- Swap relay with a known-good identical relay (if available) to verify relay function.
- Measure supply voltage at relay power terminal with ignition on and during cranking.
- Measure control signal at relay coil/ECU driver: verify expected switching (0 V or battery voltage depending on design).
Signal parameters
- Battery voltage at relay supply: nominally 11–15 V (vehicle battery voltage range).
- Relay control signal: switched by ECU — either ground-side switching (0 V to activate) or +12 V output; should show clear ON/OFF transition when heater requested.
- Relay coil resistance (typical relay): tens to a few hundred ohms (verify against replacement relay spec).
- Heater circuit current draw: potentially tens of amps when energised (varies with number/type of heaters) — use clamp meter for live measurement.
- Open-circuit: infinite/very high resistance between relay output and heater elements; short: very low resistance and excessive current.
Diagnostic algorithm
- Connect a diagnostic scanner and record DF992 / P1644 and any related codes; note freeze-frame battery voltage.
- Perform visual inspection of the relay, fuse(s) and wiring at the relay socket for corrosion, heat damage or poor connections.
- Verify battery and chassis ground voltages; repair poor grounds before further testing.
- With ignition ON, check for presence of battery voltage at relay supply terminal. If missing, inspect upstream fuse and wiring.
- Command the heater on via diagnostic tool (if supported) while monitoring the relay: listen for click and measure coil/control terminal for expected switching voltage.
- If relay does not actuate but control signal from ECU is present, replace relay and retest.
- If control signal is absent, back-probe ECU control wire and check for open/short to ground or battery; repair wiring/connector faults.
- Measure resistance/continuity from relay output to heater elements; if open or shorted, repair/replace heater elements or harness as required.
- Measure current draw of heater circuit while energized; excessive current indicates failed heater elements or short, too low may indicate open circuit.
- If wiring and components check good but fault persists, consider ECU driver fault—verify other related outputs from ECU and consult manufacturer guidance before ECU replacement.
- After repair, clear codes and repeat tests to confirm fault does not return; road/test as required.
Likely causes
- Relay failed (most common)
- Damaged connector or wiring at the relay
- Blown/poor fuse contact
- Damaged ground or supply at relay
- Heater element short or high current draw causing circuit protection
Fault status
Status
Stored fault DF992 (P1644): relay control heater 1 — control circuit abnormal (open/short/failed relay/ECU driver). Inspect relay, fuse, wiring, heater elements and ECU driver.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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