Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Mazda B4000, 2002 Mazda B3000, and 2002 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.

If QUICK TEST was not performed, go to QUICK TEST under SELF-DIAGNOSTIC SYSTEM. If QUICK TEST was performed, go to next step.
NOTE: If DTC P0402 was output during Self-Test, diagnose P0402 first before continuing with this procedure.

DTC P0505, P1504, P1507 Or Starts Only At Part Throttle: Check VPWR To IAC Valve Assembly

Disconnect IAC valve electrical connector. With KOEO, measure voltage between VPWR circuit (Red wire) at IAC valve harness connector and ground. See Fig 1 . Observe voltage. Turn ignition off. If voltage was more than 10.5 volts, go to next step. If voltage was 10.5 volts or less, repair open VPWR circuit. See WIRING DIAGRAMS article. Go to step 12 .

Fig 1: Identifying IAC Valve Harness Connector Circuits
Courtesy of MAZDA MOTORS CORP.

NOTE: During next test step, place DVOM positive lead on VPWR terminal and negative lead on IAC terminal.

Check IAC Valve Resistance

Measure resistance between VPWR terminal and IAC terminal of IAC valve. See Fig 1 . If resistance is 6-13 ohms, go to next step. If resistance is not 6-13 ohms, replace faulty IAC valve assembly. Go to step 12 .

Check IAC Valve Assembly For An Internal Short To IAC Case

Measure resistance between IAC valve circuit pin and IAC valve case. See Fig 1 . If resistance is more than 10,000 ohms:
- For DTC P1504, go to step 7 .
- For all others, go to next step.
If resistance is 10,000 ohms or less, replace faulty IAC valve. Go to step 12 .

Check Air Inlet For Plugging

Inspect air intake system for blockage or other damage. Inspect air cleaner for excessive dirt. If air intake system is okay, restore air intake system. Go to next step. If air intake system is not okay, repair as necessary. Go to step 12 .

Check For Vacuum Leaks

With KOER, listen for vacuum leaks with engine idling. Inspect air intake system from MAF sensor to intake manifold for leaks. Inspect for the following conditions:
- Air intake tube cracked or punctured.
- Air intake tube loose at air cleaner housing or throttle body.
- IAC valve assembly or gasket seal.
- EGR valve gasket.
- Vacuum supply connector and hose.
- PCV connectors and hose.
Turn ignition off. If any leaks are detected, repair as necessary. Go to step 12 . If no leaks are found, go to next step.

Check IAC Circuit Resistance

Disconnect PCM and IAC valve. Install breakout box, leaving PCM disconnected. Measure resistance of IAC circuit (White/Light Blue wire) between breakout box terminal No. 83 and IAC valve harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit. See WIRING DIAGRAMS article. Go to step 12 .

Check IAC Circuit For Short To PWR

With KOEO, measure voltage between breakout box terminal No. 83 and chassis ground. Observe voltage. Turn ignition off. If voltage is less than one volt, go to next step. If voltage is one volt or more, repair short circuit. See WIRING DIAGRAMS article. Go to step 12 .

Check IAC Circuit For Short To Ground

Disconnect scan tool from DLC. Measure resistance between breakout box terminals No. 83 (IAC circuit) and No. 103 (PWR GND circuit). If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair short circuit. Go to step 12 .
NOTE: During next step, if engine is stalling, place a shim under the hard stop screw to maintain idle. During test procedure, if closed throttle RPM is significantly higher than normal, go to step 11 .

Check IAC Signal From PCM

Remove breakout box. Reconnect PCM and IAC valve. With KOER, select Diagnostic Data Link. Select PCM. Select PID Monitor and Record. Access IAC and RPM PIDs. With engine at normal operating temperature, all accessories off, and throttle closed, IAC duty cycle must be approximately 22-45 percent. Observe IAC duty cycle. Slowly increase engine speed to 3000 RPM and return to closed throttle. Observe IAC duty cycle. If IAC duty cycle is within specification at closed throttle and duty cycle responds to RPM change:
- For Continuous Memory DTCs P1504 and P1507, go to next step.
- For all others, turn ignition off. Inspect throttle body for damage. Repair as necessary. Go to step 12 . If throttle body is okay, replace faulty IAC valve. Go to step 12 .
If IAC duty cycle is not within specification at closed throttle and/or duty cycle does not respond to RPM change:
- For DTC P1507, replace faulty IAC valve. Go to step 12 .
- For all others, replace faulty PCM. Go to step 12 .

Check IAC System For Intermittent Open Or Short

Using scan tool, select Diagnostic Data Link. Select PCM. Select PID Monitor and Record. Access IAC and RPM PIDs. Observe PIDs for an indication of a fault while performing the following at idle:
- Lightly tap on IAC valve and wiggle harness connector to simulate road shock.
- Grasp vehicle harness closest to IAC valve. Shake and bend a small section of wiring harness from IAC valve to dash panel, and from dash panel to PCM connector.
If IAC and RPM PIDs suddenly change in value indicating a fault, isolate fault and repair as necessary. Go to next step. If IAC and RPM PIDs do not suddenly change in value:
- For idle quality, starting or stalling problems, replace faulty IAC valve. Go to next step.
- For all others, fault is not present at this time. See INTERMITTENT under SYSTEM TESTS.

Verify Trouble Shooting Of DTCs Completed

Reconnect all electrical connectors. Perform QUICK TEST under SELF-DIAGNOSTIC SYSTEM. If same DTC is present, replace faulty PCM. Repeat QUICK TEST under SELF-DIAGNOSTIC SYSTEM. If any other DTC is present, go to applicable procedure for other DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are set, trouble shooting is complete.