What Does P1618 Mean?
The glow plug or grid heater relay control circuit is shorted to battery positive voltage. This prevents the ECM from properly controlling the relay that powers the glow plug or intake air heater system.
Common Causes
35%
Shorted glow plug relay with internal contacts stuck closed or coil shorted to power pin
30%
Damaged wiring between ECM and glow plug relay creating short to battery voltage
20%
Crossed wires in relay socket or connector causing short to power circuit
10%
Incorrect relay installation with wrong relay type causing power feedback
5%
ECM internal short circuit in relay driver output stage
Diagnostic Steps
1
Step 1: Locate and remove glow plug relay from relay box; inspect relay and socket for damage, melting, or corrosion
2
Step 2: With relay removed, measure voltage on relay control wire from ECM (should be 0V with key on, relay command off)
3
Step 3: Install new relay temporarily and use scan tool to command relay on/off while monitoring for proper operation
4
Step 4: Check for voltage on relay control circuit with ECM connector disconnected (should be 0V); voltage present indicates wiring short
5
Step 5: Trace relay control wire from ECM to relay socket checking for damaged insulation, pinch points, or contact with power sources
Estimated Repair Cost
$120 - $500
Parts + labor, varies by vehicle and location
The glow plug or grid heater relay control circuit is shorted to battery positive voltage. This prevents the ECM from properly controlling the relay that powers the glow plug or intake air heater system.
The most common cause of P1618 (Glow Plug/Heater Relay Circ. Short to B+) is: Shorted glow plug relay with internal contacts stuck closed or coil shorted to power pin
Typical repair costs for P1618 range from $120 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Moderate concern; glow plugs may remain energized continuously causing premature failure or potential overheating. Diesel engines may experience hard starting or no-start in cold weather.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1618 to identify the root cause.
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Quick Info
Category
Powertrain
System
Glow Plug System / Cold Start System
Difficulty
Type
Manufacturer
Recommended Tools
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