Diagnostic Aids

WARNING: This page is about a different car, the 1995 Mazda MX-6 and 1995 Mazda 626. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test when directed by QUICK TEST. PCM uses adaptive fuel logic to compensate for normal variances in fuel system components. If fuel system appears to be too rich or too lean, adaptive fuel will make appropriate shift in fuel delivery calculations to compensate.

1) Continuous Memory Codes 179 & 181 Code 179 identifies a rich fuel condition resulting in adaptive fuel strategy leaning fuel system to compensate. Code 181 identifies a lean fuel condition resulting in adaptive fuel strategy enriching fuel system to compensate. Possible causes for these codes are:

Incorrect fuel pressure.
Faulty fuel injector or circuit.
Leaking or restricted air intake.
Restricted air or fuel filter.

If other codes are present, repair as necessary. If no other codes are present, go to next step.

2) Check Fuel Pressure Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Ensure manifold vacuum supply is connected to fuel pressure regulator (if equipped). Run engine at idle and check fuel pressure. See FUEL PRESSURE SPECIFICATIONS table. If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, check and repair fuel system as necessary. See FUEL SYSTEM in appropriate TESTS W/CODES - 2.0L M/T article.

FUEL PRESSURE SPECIFICATIONS

Engine	KOER Pressure psi (kg/cm² )	KOEO Pressure psi (kg/cm² )
2.0L A/T	30-38 (2.1-2.7)	37-46 (2.6-3.3)

3) Check System Ability To Hold Fuel Pressure Cycle ignition on and off several times. Check fuel system for leaks. Repair or replace as necessary. Pressurize fuel system. See FUEL PRESSURE SPECIFICATIONS table. If fuel system does not leak and pressure remains at specification for 5 minutes, go to next step. If fuel pressure is not within specification, check and repair fuel system as necessary. See FUEL SYSTEM in TESTS W/CODES - 2.0L M/T article.

4) Cylinder Balance Test Perform KOER SELF-TEST. After last code is displayed, wait 5-10 seconds. Enter CYLINDER BALANCE TEST by lightly goosing throttle (not WOT). Test time is about 2-3 minutes. If cylinder balance test service Code 90 is not present, go to next step. If cylinder balance test service Code 90 is present, check and repair ignition system as necessary. See IGNITION SYSTEM in SYSTEM/COMPONENT TESTS - 2.0L article.

5) Check Injector & Harness Resistance Turn ignition off. Disconnect PCM 60-pin connector and inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install Breakout Box (49-UN01-058), leaving PCM disconnected. Measure and record resistance between suspected injector circuit test pin and test pin No. 37 at breakout box. See INDIVIDUAL INJECTOR RESISTANCE table. If each resistance is within specification, go to step 8). If resistance is not as specified, go to next step.

INDIVIDUAL INJECTOR RESISTANCE @ 68°F (20°C)

Engine	Ohms
2.0L A/T	12-16

6) Check Fuel Injector Harness Continuity Turn ignition off. Disconnect suspect fuel injector wiring harness connector. Set DVOM to 200-ohm scale. With breakout box installed and PCM disconnected, measure resistance between test pins No. 37 and 57 at breakout box and VPWR terminal at suspect injector wiring harness connector. Also, measure resistance between injector test pin(s) at breakout box and same injector circuit terminal at each injector wiring harness connector. If each reading is less than 5 ohms, go to next step. If each reading is 5 ohms or more, repair open circuit. Remove breakout box, reconnect all components and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

7) Check Injector Harness Circuit For Short To Power Or Ground Turn ignition off. With breakout box installed and PCM disconnected, disconnect suspect fuel injector wiring harness connector. Measure resistance between injector test pin(s) and test pins No. 37, 40, 46, 57 and 60 at breakout box. Also, measure resistance between injector test pin(s) at breakout box and chassis ground. If each resistance is 10,000 ohms or more, replace injector per cylinder balance test service code and repeat QUICK TEST. See CYLINDER BALANCE TEST SERVICE CODES table to interpret codes. If each resistance is less than 10,000 ohms, repair short circuit. Remove breakout box, reconnect all components and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

CYLINDER BALANCE TEST SERVICE CODES

Service Code	Application
90	Pass
10	Cylinder No. 1
20	Cylinder No. 2
30	Cylinder No. 3
40	Cylinder No. 4
538	Retest

8) Check Injector Drive Signal Turn ignition off. With breakout box installed, connect PCM to breakout box. Using a non-powered 12-volt test light, connect test light between test pin No. 37 and suspect fuel injector test pin at breakout box. Crank or start engine. If test light glows dimly, system is operating correctly. Remove breakout box and reconnect all components. Also check ignition system for other possible problems. See IGNITION SYSTEM in SYSTEM/COMPONENT TESTS - 2.0L article. Drive vehicle for 5 miles at 55 MPH and repeat QUICK TEST and CYLINDER BALANCE TEST. If test light does not glow dimly (no light/bright light), replace PCM. Remove breakout box, reconnect all components and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.