643

Possible Causes

• •Wire connected to terminal # 19 at the ECM is partially or completely shorted to power (Vbat, Vsw, Vrelay, etc)
• •Poor ECM ground
• •Faulty ECM
• •Intermittent problem
• •Poor connection at sensor
• •Faulty MAP sensor
• •5 volt reference higher than 5.40 volts
• •Sensors or components powered by the 5 volt supply are overloaded, shorted, or out of specification
• •Wire connected to terminal # 19 at the ECM is partially or completely shorted to power (Vbat, Vsw, Vrelay, etc >)

Suggested Actions

1. 1Perform the On-Board (OBD) System Check
2. 2Key ON, Engine Running, System Mode = 'Running' and check if DTC 643 displays
3. 3Using DST, check if 5Vext1 FB (VE5a_FB_raw) * 11/10 < 0.10 VDC
4. 4Using a DMM, measure the voltage potential across 5ref1 and 5V rtn1 at connector to check if voltage is >4.7 VDC
5. 5If DTC 642 or 643 are present, troubleshoot those first
6. 6Jumper the MAP circuit to Vref (5 VDC) in connector on harness to check if DST displays MAP voltage of 4.7 VDC or greater
7. 7Disconnect wire harness header from ECM, carefully remove yellow lock from header at device output terminal, and check if resistance between MAP input at ECM header and signal at device is <5 ohms (probe on the side of terminal; do not insert probe or object into terminals to avoid spreading pins)

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