The P1687 code on your 2020 Jeep Wrangler indicates an internal error within the powertrain control module (PCM). This Stellantis-specific code affects your Wrangler's 2.0L turbocharged 4-cylinder or 3.6L Pentastar V6 engine's primary computer, signaling the PCM has detected an internal malfunction that may affect its ability to control engine functions properly.
Understanding P1687 on Wrangler
The PCM is the main computer controlling engine operation, transmission, and emissions systems. Code P1687 sets when the PCM's internal self-diagnostic routines detect a fault within its own processors, memory, or circuits. This is a serious code that may indicate PCM replacement is needed, though other causes should be ruled out first.
Common Symptoms
- Check engine light on
- Multiple unrelated codes stored
- Erratic engine behavior
- Stalling or no-start conditions
- Poor fuel economy
- Transmission shifting problems
- Various warning lights illuminated
- Loss of communication with scan tool (in severe cases)
Primary Causes
- Actual PCM internal failure
- PCM power supply or ground issue
- Low battery voltage causing PCM errors
- Water intrusion into PCM
- Corroded PCM connectors
- Software/calibration corruption
- Aftermarket tuning or flash issues
- Electrical system voltage spikes
Diagnostic Procedure for 2020 Wrangler
Before condemning the PCM, verify battery voltage is stable (12.4V+ with key off, 13.5-14.8V running). Check PCM power and ground circuits for proper voltage and continuity. Inspect PCM connectors for corrosion, water intrusion, or bent pins. Attempt PCM software update or reflash if available. Check for aftermarket devices that may conflict with PCM operation. Monitor for voltage spikes or electrical interference.
Repair Solutions
Address any power, ground, or connector issues found. If battery or charging system problems caused PCM errors, resolve those first and clear codes. Attempt PCM reflash if corruption is suspected. Remove aftermarket tuning devices if recently installed. If all external causes are eliminated and P1687 returns after clearing, PCM replacement and programming is required. Use only OEM or verified remanufactured PCMs.