X120 - Road Test

The purpose of the road test is to identify an area of concern by monitoring certain controlled parameters while trying to re-create a driveability or 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, PCM connected.

- Install fuel pressure gauge and MAP/BARO tester (optional).

- Other materials needed; 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>1O.5V (Pin 1), VPWR>1O.5V (Pins 37/57), VREF 5±1V (Pin 26).

GROUNDS: (all = 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 NEEDED INFORMATION AND MATERIALS BEFORE THE ROAD TEST

- Refer to the Symptom Charts in Intermittent Fault Diagnosis, looking at the chart(s) that most resembles the vehicle's 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, along with the FP/FPM signal(s), are the main signals that will be monitored.

- Refer to the proper Diagnostic Reference Value Sheet in Specifications. Specifications
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 Hz using the MAP/BARO tester). Also refer to EEC Graphs and Charts. Graphs and Charts

- The use of test lamp(s) and a DVOM may also aid diagnosis. Depending on the DTC being diagnosed, the FP/FPM circuits could be monitored as well as the circuits to/from the Inertia Fuel Shutoff switch, the Left/Front 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 recommended 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.

- Drive the vehicle to create the conditions so that the symptom will occur. If the Customer Information Worksheet has been completed, this information may help when trying to re-create the symptom.

- When the symptom occurs, the accompanying passenger should observe changes in listed PCM signals. Information about the symptom, operating condition value of the PCM signal or other notes should be record onto paper.

- If you are unable to duplicate the symptom, it may still be helpful to verify that the PCM values are in the expected range.

ANALYZING THE DATA

- Once the road test is completed, the results need to be analyzed to locate and service the exact fault which caused the symptom.

- If no problem is identified, return to Diagnostic Routines for other possible causes of the symptom.