Hyundai Coupes/Sedans 1986-1993 Repair Guide

Diagnosis and Testing



Never disconnect any electrical connection with the ignition switch ON unless instructed to do so in a test.
Always wear a grounded wrist static strap when servicing any control module or component labeled with a Electrostatic Discharge (ESD) sensitive device symbol.
Avoid touching module connector pins.
Leave new components and modules in the shipping package until ready to install them.
Always touch a vehicle ground after sliding across a vehicle seat or walking across vinyl or carpeted floors to avoid static charge damage.
Never allow welding cables to lie on, near or across any vehicle electrical wiring.
Do not allow extension cords for power tools or drop lights to lie on, near or across any vehicle electrical wiring.
Do not operate the cruise control or the engine with the drive wheels off the ground unless specifically instructed to do so by a test procedure.


The cruise control system performs control functions for the setting or cancellation of the fixed speed driving speed based upon the data provided by input signals. As a result, when the cruise control system is canceled, the cause of cancellation is memorized in a separate circuit by the ECU, regardless of whether or not the cruise control system condition is normal or abnormal, thus providing the ECU with the self diagnosis function by certain fixed patterns as well as the function of being able to check whether or not the ECU's input switches or sensor are normal. Thus, by effectively using these functions, the time required checking and repairing the system can be shortened.

When the ECU power supply (ignition switch and main switch) is switched OFF, the memorized trouble codes are erased, and so for this reason the power supply must be left ON until the checking is completed.


The self-diagnosis checking is performed when there has been an automatic cancellation, without cancel switch operation. The following 2 methods can be used for checking diagnosis. Note that the diagnosis check connector is located in the fuse box.

Multi-Use Tester Tool Method

See Figures 1 and 2

  1. Connect the multi-use tester's (09391-33000 or equivalent) socket and connector to the cigarette lighter socket and the self-diagnosis check connector and set the tester.
  3. Use the tester according to its operation instructions; display the diagnosis code number and then check.

Click image to see an enlarged view

Fig. Fig. 1: Connecting the tester to the vehicle for speed control diagnosis

Voltmeter Method

Connect a voltmeter between the ground terminal and the terminal of for the cruise control of the diagnosis connector. It is possible to discover which circuit is the cause of the cancellation by verifying the indication shown on the voltmeter with the display patterns.

When trouble codes number 11, 12, 15 or 16 are displayed, check the troubleshooting symptom applicable to that number.

Code number 16 is entered in the memory as cancel switch ON signal input if the system is canceled by depressing the brake pedal, and code number 13 or 14 is entered when there is an automatic cancellation because the vehicle speed drops when the vehicle is driven up a steep slope with the preset speed setting left set etc., when however, there is a cancellation not intentionally made by the driver, the cause might be a damaged or disconnected stop lamp switch input wiring, a malfunction of the stop lamp switch ON, etc., even though the same code number 16 is displayed.

Click image to see an enlarged view

Fig. Fig. 2: Sample display pattern for code 23

Troubleshooting Procedures

First, select the applicable malfunction symptom from the trouble symptom charts. Conduct the self-diagnostic test following the directions on the charts. Determine the condition of all function circuits by making the following preliminary inspections:

Because the computer (self-diagnosis) memory data will be erased, when the system is unintentionally canceled during fixed speed driving, the ignition switch and/or the cruise main switch of the cruise control system should not switched OFF, and the battery should not be disconnected.

  1. Check that the installation of actuator, accelerator cables are correct, and that the cables and links are securely connected.
  3. Check that the accelerator pedal moves smoothly.
  5. Adjust the cable so there is no excessive tension or excessive play on the accelerator cable.
  7. Check that the ECU, actuator, cruise main and control switch and the connector of each cancel switch are connected securely.
  9. Check in the sequence indicated in the trouble symptom chart.
  11. If these checks indicate a normal condition, replace the cruise control unit.

Codes indicated by the * symbol are displayed, if the conditions are satisfied, even if the system is normal. In either case, the system is normal if can be reset. If there is an automatic cancellation not intentionally made by the driver, however, excluding cancellations explicitly made by a cancel procedure, there may be a temporary malfunction such as a poor contact of a harness connector even though the system can be reset, and for that reason it is necessary to check according to each individual check the chart that is applicable.

Diagnosis codes are display when, after cancellation of the cruise control system, the vehicle speed decreases to less than approximately 12 mph, and are erased by switching OFF the ignition switch or the MAIN switch. After the diagnosis codes in memory are erased, if (when power supply of the electronic control unit is switched ON once again) the power supply of the electronic control unit is normal, the diagnosis output code display will be as follows; regardless of whether the system condition is normal or not.

If a multi-use tester is used, NORMAL will be displayed. If a voltmeter is used, continuous ON/OFF signals will be displayed at 0.5 second intervals.