Identifying Vehicle Communication Problems

Battery must be fully charged before proceeding. Connect scan tool to Data Link Connector (DLC) to retrieve messages. Ensure ground circuit has continuity at terminal No. 4 on DLC. Ensure 12 volts exists at terminal No. 16 on DLC. See following list of vehicle communication symptoms and scan tool fault messages. Proceed to appropriate test. Always turn ignition off prior to disconnecting any module connector.

• BUS (+) & BUS (-) SHORTED TOGETHER 
• BUS BIAS LEVEL TOO HIGH (CHEROKEE) 
• BUS BIAS LEVEL TOO HIGH (WRANGLER) 
• BUS BIAS LEVEL TOO LOW (CHEROKEE) 
• BUS BIAS LEVEL TOO LOW (WRANGLER) 
• BUS (+) & BUS (-) OPEN 
• BUS (+) OPEN OR BUS (-) OPEN 
• SCAN TOOL BLANK SCREEN 
• NO BUS BIAS (CHEROKEE) 
• NO BUS BIAS (WRANGLER) 
• NO RESPONSE FROM AIRBAG CONTROL MODULE (CHEROKEE) 
• NO RESPONSE FROM AIRBAG CONTROL MODULE (WRANGLER) 
• NO RESPONSE FROM COMPASS MINI-TRIP COMPUTER (CMTC) 
• NO RESPONSE FROM INSTRUMENT CLUSTER 
• NO RESPONSE FROM POWERTRAIN CONTROL MODULE (PCM) 
• NO RESPONSE FROM REMOTE KEYLESS ENTRY (RKE) 
• NO RESPONSE FROM SENTRY KEY IMMOBILIZER MODULE (SKIM) 
• NO RESPONSE FROM TRANSMISSION CONTROL MODULE (TCM) 
• NO TERMINATION 
• NOT RECEIVING BUS MESSAGES CORRECTLY 
• SHORT TO 5 VOLTS 
• SHORT TO BATTERY 
• SHORT TO GROUND