Diagnostic Aids
Enter this test when directed by QUICK TEST. This test is only intended to diagnose:
* Harness circuits (SIG RTN and OCT ADJ).
* Octane adjust shorting bar connector.
Purpose of Octane Adjust Shorting Bar is to provide optimum spark advance for fuel used. If engine detonates (spark knock), remove Octane Shorting Bar. This retards spark advance about 3-4 degrees. If engine continues to detonate, use fuel with a higher octane rating.
1) DTC P1390
This code indicates Octane Adjust (OCT ADJ) shorting bar is not in place or OCT ADJ circuit is open. Turn ignition off. Inspect Octane Adjust in-line connector. If shorting bar has been removed, go to next step. If shorting bar is in place, go to step 4).
2) Check For Modification Decal
If vehicle has modification decal indicating OCT ADJ shorting bar was removed as a factory authorized procedure, testing is complete. If engine is detonating, go to TROUBLE SHOOTING (EEC-V) - NO CODES article. If vehicle does not have modification decal, go to next step.
3) Check For DTC P1390
Replace OCT ADJ shorting bar. Perform KOEO SELF-TEST. If DTC P1390 is present, go to next step. If DTC P1390 is not present, testing is complete. If there are no codes and driveability faults are present, go to TROUBLE SHOOTING (EEC-V) - NO CODES article.
4) Check Octane Adjust Circuit Continuity
Continuity should exist from OCT ADJ circuit, through in-line connector and shorting bar, to SIG RTN circuit. Turn ignition off. Disconnect 104-pin PCM connector. Inspect connector for damage and repair as necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. Measure resistance between test pin No. 30 (OCT ADJ) and 91 (SIG RTN) at breakout box. If resistance is less than 5 ohms, replace PCM and repeat QUICK TEST. If resistance is 5 ohms or more, repair open OCT ADJ circuit, shorting bar or SIG RTN circuit. Repeat QUICK TEST.
5) Check For DTC P1390
Start engine. Warm it to normal operating temperature. Turn ignition off. Perform KOEO SELF-TEST. If DTC P1390 is not present, go to next step. If DTC P1390 is present, return to step 1).
6) Verify In-Line Shorting Bar Is Installed
Turn ignition off. Inspect OCT ADJ in-line connector. If shorting bar is installed, go to step 8). If shorting bar is not installed, go to next step.
7) Check For Modification Decal
If vehicle has modification decal indicating OCT ADJ shorting bar was removed as a factory authorized procedure, go to step 10). If vehicle does not have a modification decal, replace shorting bar. If engine is detonating, go to TROUBLE SHOOTING (EEC-V) - NO CODES article.
8) Check For Technical Service Bulletin (TSB)
If a TSB authorizing removal of OCT ADJ shorting bar exists, go to next step. If a TSB authorizing removal of OCT ADJ shorting bar does not exist, testing is complete. If engine is detonating, go to TROUBLE SHOOTING (EEC-V) - NO CODES article.
9) Remove OCT ADJ Shorting Bar
Turn ignition off. Remove OCT ADJ shorting bar. Test drive vehicle to verify complaint. If detonation is present, go to next step. If detonation is not present, testing is complete.
10) Check Octane Adjust Circuit For Short To Ground
Turn ignition off. Disconnect 104-pin PCM connector. Inspect connector for damage and repair as necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. Measure resistance between OCT ADJ terminal at in-line connector and test pins No. 51, 91 and 103 at breakout box. If each resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair short circuit. If engine is still detonating, go to TROUBLE SHOOTING (EEC-V) - NO CODES article.
11) Check PCM
Turn ignition off. Disconnect OCT ADJ shorting bar. Connect PCM to breakout box. Turn ignition on. Measure voltage between breakout box OCT ADJ terminal of in-line connector and test pins No. 51 and 103. If voltage is less than 4 volts, replace PCM. If voltage is 4 volts or more, remove breakout box. If engine is still detonating, go to TROUBLE SHOOTING (EEC-V) - NO CODES article.