X120 - Road Test
The purpose of the road test is to identify an area of concern by monitoring certain controlled parameters while trying to recreate a driveability or Malfunction Indicator Light (MIL) symptom.
NOTE: A basic working knowledge of the EEC-IV system is critical to effectively analyze road test data.
WARNING: This road test is a suggested but optional procedure. All applicable safety procedures and traffic laws must be followed. In order for a road test to be performed, it is required that another person accompany the driver. The accompanying person can make measurements, observe changes and record notes. If for some reason this test is not performed, return to diagnostic routines for other possible causes.
Prepare Vehicle For A Road Test
- Install breakout box, if applicable.
- Breakout box installed, Powertrain Control Module (PCM) connected.
- Install fuel pressure gauge and Manifold Absolute Pressure (MAP) / Barometric Pressure (BARO) tester (optional).
- Other materials needed; Digital Volt/Ohm Meter (DVOM), pencil, paper, appropriate schematic/pin usage sheet.
Preliminary Power/Ground Checks
- With the key ON and a DVOM referenced to the battery negative post, check the following signals for correct values.
POWERS:
KAPWR >10.5V (Pin 1)
VPWR >10.5V (Pins 37/57)
VREF 5 (+/-) 1V (Pin26)
GROUNDS: (all = 0 (+/-) 0.5V)
PWR GND (Pins 40/60)
SIG RTN (Pin 46)
IGN GND (Pin 16)
OPTIONAL GROUNDS:
HO2S GND (Pin 49)
CSE GND (Pin 20)
MAF RTN (Pin 9 or 15)
Obtaining Other Information And Materials Before The Road Test
- Refer to the Symptom Charts in Diagnosis by Symptom (Diagnostic Routines) that most resemble the driveability or MIL symptom. Before the road test, perform the Visual/Mechanical Checks that are listed. Next, list the PCM sensors and actuators in the order given. These circuits and the Fuel Pump (FC) / Fuel Pump Monitor (FPM) signal(s) are the main signals that will be monitored.
- Refer to the proper Diagnostic Reference Value. Although these charts were designed for use with the EEC-IV monitor box, most of the values can be read using the breakout box and a DVOM (with the DVOM referenced to ground, all values in DCV units can be used; other values may also be helpful, ex., MAP frequency using the MAP/BARO tester). Also refer to Graphs and Charts.
- The use of test lamp(s) and a DVOM may also aid diagnosis. Depending on the Diagnostic Trouble Code (DTC) being diagnosed, the FP/FPM circuits could be monitored, as well as the circuits to/from the Inertia Fuel Shutoff switch, the Left 1 Front Heated Oxygen Sensor (HO2S) circuit, etc. Remember, if the vehicle stalls, the PCM will "unground"the FP circuit and turn off the fuel pump. If the problem is in the fuel pump wiring, the lamp/voltage should change just before the symptom occurs.
NOTE: Due to the low resistance of some test lamps, it is required that a DVOM or equivalent high resistance testing device be used when monitoring PCM output circuits.
Road Test
- After starting the engine for the road test, enter Engine Running Continuous Monitor Diagnostic Test Mode. Output State Diagnostic Test Mode
- Drive the vehicle to create the conditions in which the symptom occurs. If the Customer Information Worksheet has been completed, this information may help in recreating the symptom.
- When the symptom occurs, the passenger should observe changes in listed PCM signals. Information about the symptom, operating condition, value of the PCM signal or other notes should be recorded.
- If the symptom cannot be duplicated, verify that the PCM values are in the expected range.
Analyzing The Data
- Once the road test is completed, the results should be analyzed to locate and service the fault which caused the symptom.
- If no problem is identified, return to Diagnostic Routines for other possible causes of the symptom. Symptom Related Diagnostic Procedures