I copied these off my factory manual CD for a '99. Hopes this helps cause it took me a while to do. I don't know what some of the abbriviations mean and I can't find them on my CD sorry.
p0340: The test fails when the PCM can no longer detect the from the CMP sensor.
Possible causes:
-CMP circuit open
-CMP circuit short to ground
-CMP circuit short to power
-SIG RTN open (VR sensor)
-CMP GND open (Hall effect sensor)
-CMP misinstalled (Hall effect sensor)
-Damaged CMP sensor shielding
-Damaged CMP sensor
-Damaged PCM
Diagnostic Aides:
Harness routing, harness alterations, improper shielding, or electrical interference from other improperly functioning systems may have intermittent impact on the CMP signal.
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p0402: The EGR system is monitored for undesired EGR flow during idle. The EGR monitor looks at the DPF EGR signal at idle and compares it to the stored signal measured during key ON and engine OFF. The test fails when the signal at idle is greater than at key ON engine OFF by a calibrated amount.
Possible causes:
-EGR valve stuck open.
-Plugged EGR vacuum regulator solenoid vent
-Plugged EGR tube
-Slow responding DPF EGR sensor
-Damaged DPF EGR sensor
-Improper vacuum hose connection
-Plugged vacuum hoses
-EGRVR circuit shorted to ground
-Damaged EGR vacuum regulator solenoid
-Damaged PCM
Diagnostic Aides:
A DPFEGR PID reading that is greater at idle than during key ON and engine OFF by 0.5 volt or a rough engine idle, may indicate a hard fault.