Code
P1635
DAEWOO
P — Powertrain
Wts heater relay fault
Views:
UK: 11
EN: 14
RU: 10
AI status
Completed
Completed
100%
Causes
- Failed or sticking WTS heater relay (contacts or coil)
- Blown fuse for the heater circuit
- Open, shorted or high-resistance wiring between relay, heater element and control module
- Corroded or loose connectors or poor ground at relay/heater
- Faulty heater element (load) causing abnormal relay behavior
- Faulty engine control module (ECM/BCM) driver output for the relay
Symptoms
- WTS heater does not operate or intermittent operation
- Related heater or engine warm-up performance worse than expected
- Possible warning lamp or message relating to heater or system
- Stored fault code(s) and inability to actuate relay with scan tool
What to check
- Read freeze-frame and stored data with a scan tool; note any additional codes
- Visual inspection of relay, fuse(s), wiring harness and connectors for damage or corrosion
- Verify presence and correct part number of the WTS heater relay in relay box
- Check fuses related to heater circuit for continuity
- Attempt to actuate the relay from a scan tool or by applying battery voltage to relay coil
- Backprobe relay connector to measure command voltage and ground when relay is commanded
Signal parameters
- Control/command: battery voltage (~12 V) present at relay coil terminal when commanded ON
- Coil resistance: typically tens to a few hundred ohms (check service data for exact value)
- Switched output: near battery voltage at relay output terminal when relay is energized
- Load path: low resistance between relay output and heater element (ohms range dependent on heater)
- Ground: near 0 Ω continuity from heater ground to chassis ground
Diagnostic algorithm
- Retrieve all DTCs and freeze-frame info; record conditions when P1635 set. Clear codes and attempt to reproduce.
- Perform a thorough visual inspection of relay, fuse, connectors and wiring for obvious damage, corrosion or loose pins.
- Check and replace any blown fuses related to the heater circuit. Re-test for code reappearance.
- Identify the WTS heater relay socket terminals using the vehicle wiring diagram. With key ON (or commanded via scan tool), backprobe coil terminals and confirm control voltage is present when the module requests relay ON.
- Measure relay coil resistance with relay removed. If coil is open or out of specification, replace relay.
- With relay energized, measure voltage at relay output terminal. If relay output does not reach battery voltage, replace relay or repair relay power feed/ground.
- Check continuity and resistance of wiring between relay output and heater element, and between heater element and ground. Repair any opens or high-resistance connections.
- Swap relay with a known-good identical relay (if available) to check for functional change.
- If wiring and relay are good but command signal from control module is missing or abnormal, inspect connectors and grounds at the module. If wiring to module is good, consider module driver failure and consult manufacturer repair procedures before replacing module.
- After repairs, clear codes and perform functional test and/or road/test cycle to confirm proper operation and ensure code does not return.
Likely causes
- Relay coil open or contacts fused/worn
- Blown or intermittent fuse protecting the heater circuit
- Wire chafing and short to ground or battery (or open circuit)
- Connector corrosion or pin pushed out at relay socket
- High resistance in ground or supply feed causing undervoltage at relay
- Control module not commanding relay due to internal fault or software
Fault status
Status
WTS heater relay circuit fault detected — relay failed to operate or control circuit out of specification.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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