What Does P1636 Mean?
The PCM is not receiving the correct start enable signal from the theft deterrent system, or the main relay that provides power hold functionality has failed. This prevents proper PCM operation or engine starting.
Safety Warning
Vehicle may fail to start or shut down unexpectedly, potentially stranding driver in unsafe locations.
Common Causes
30%
Faulty main relay (power hold relay) causing intermittent power supply to PCM
25%
Communication failure between immobilizer/security module and PCM
20%
Key fob or transponder chip not recognized by theft deterrent system
15%
Corroded or loose relay socket connections causing intermittent power
10%
PCM or security module software requires reprogramming or synchronization
Diagnostic Steps
1
Step 1: Attempt to start vehicle and observe theft deterrent system indicator light behavior during cranking
2
Step 2: Locate and test main relay (PCM power hold relay) for proper operation - check for clicking and continuity when energized
3
Step 3: Use scan tool to check for communication between security module and PCM, verify immobilizer status
4
Step 4: Check power and ground circuits to main relay and PCM with voltmeter, including relay socket condition
5
Step 5: Verify key is properly programmed to vehicle; if all circuits test normal, PCM or security module may require programming or replacement
Estimated Repair Cost
$150 - $1,200
Parts + labor, varies by vehicle and location
The PCM is not receiving the correct start enable signal from the theft deterrent system, or the main relay that provides power hold functionality has failed. This prevents proper PCM operation or engine starting.
The most common cause of P1636 (Theft Deterrent Start Enable Signal Not Correct/ Main Relay Malfunction (Power Hold)) is: Faulty main relay (power hold relay) causing intermittent power supply to PCM
Typical repair costs for P1636 range from $150 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may fail to start or shut down unexpectedly, potentially stranding driver in unsafe locations.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1636 to identify the root cause.
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Quick Info
Category
Powertrain
System
Anti-Theft System / PCM Power Supply
Difficulty
Type
Manufacturer
Recommended Tools
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