J99 - 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, processor 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 >10.5V (Pin 1), VPWR > 10.5V (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: HEGO 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 Diagnosis by Symptom Charts looking at the chart(s) that most resembles the vehicle's driveability or MIL light symptom. Before the road test perform the Visual/Mechanical Checks that are listed. Next, list the EEC-IV 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. 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).

- The use of test lamp(s) and a DVOM may also aid diagnosis. For example, with a Continuous Memory 87/556 (fuel pump primary circuit failure) and a surge/stall symptom, a test lamp could be connected at the fuel pump relay between the VPWR circuit and ground, with a DVOM connected between the Fuel Pump (FP) circuit at the relay and Test Pin 1 (KAPWR) at the breakout box. Under normal drive conditions the lamp will be on and the DVOM will read battery voltage (if the vehicle stalls, the processor will "unground" the FP circuit and the DVOM voltage will be low. If the problem is in the fuel pump wiring the lamp/voltage should change just before the symptom occurs). If the VPWR lamp goes out, the problem is in the VPWR supply to the relay. If the lamp stayed on, the DVOM voltage remained high and a Continuous Memory 87/556 was set again, REPLACE the fuel pump relay. If only the FP voltage went low, the problem is either in the FP circuit or the processor. The DVOM could now be connected between Test Pin 22 (FP) and Test Pin 1 (KAPWR) at the breakout box. If, just before the symptom occurs, the voltage goes low, REPLACE the processor; if the voltage stays high, the problem is in the FP circuit wiring. For the fuel pump secondary circuit codes (95/542, 96/543), the BATT(+), Power-to-Pump and FPM circuits could be similarly monitored.

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 processor output circuits.

Road Test

- After starting the engine for the road test, enter Engine Running Continuous Memory 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 EEC-IV signals. Information about the symptom, operating condition value of the EEC-IV signal or other notes should be recorded onto paper.

- If you are unable to duplicate the symptom, it may still be helpful to verify that the EEC-IV 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.