Let start with the P1574 and P0128 since they are the ones that came on first.
DTC P1574: ASCD VEHICLE SPEED SENSOR
ECM receives vehicle speed signals via 2 different lines, and detects vehicle speed for ASCD control. Vehicle speed signals are input from instrument cluster and Transmission Control Module (TCM) separately. Signal from TCM is via CAN communication line.
Malfunction is detected when ECM detects a difference in values between the 2 vehicle speed signals. Possible causes are:
CAN communication line open or shorted.
Instrument cluster circuit open or shorted.
Defective instrument cluster.
Defective vehicle speed sensor.
DTC Confirmation Test
Start engine. Ensure TCS is turned off. Select DATA MONITOR mode with scan tool. Drive vehicle at more than 25 MPH. If 1st trip DTC is detected, go to DIAGNOSTIC PROCEDURE. If 1st trip DTC is not detected, system is okay at this time.
1. Check for A/T system DTCs. If problem is found, diagnose A/T system. If problem is not found, go to next step.
2. Check VSS, VSS circuit and instrument cluster. Repair as necessary.
DTC P0128: THERMOSTAT FUNCTION
Malfunction is detected when engine coolant temperature has not risen enough to open thermostat even though engine has run long enough. Possible causes are:
Thermostat stuck open.
Leakage from sealing portion of thermostat.
Defective ECT sensor.
DTC Confirmation Test
1. Replace thermostat with an OEM replacement. Turn ignition on. Select COOLAN TEMP/S in DATA MONITOR mode with scan tool. If COOLAN
TEMP/S is less than 140 F (60 C), go to next step. If COOLAN TEMP/S is not less than 140 F (60 C), allow engine to cool.
2. Drive vehicle at a speed of 50-75 MPH for 10 consecutive minutes. If 1st trip DTC is detected, go to DIAGNOSTIC PROCEDURE. If 1st trip DTC is not detected, system is okay at this time.
Remove ECT sensor, and place in heated water. Measure resistance between sensor terminals, with water at specified temperatures.
See ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE table. If resistance is as specified, test is omplete.
If resistance is not as specified, replace ECT sensor.
Monday, November 7th, 2011 AT 5:17 PM