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 only when directed by QUICK TEST. This test is intended to diagnose:

TP sensor.
Wiring harness circuits (TP, SIG RTN and VREF).
Powertrain Control Module (PCM).

Normal range of throttle angle measurement for TP sensor is 0-85 degrees. To pass QUICK TEST procedure, range of throttle rotation (in degrees) must be within 3 percent of specification.

To prevent replacement of good components, be aware the following non-EEC related areas may be at fault:

Idle speed.
Binding throttle shaft or linkage.
TP sensor not seated.

1) KOER Code 121: Check For Other Codes KOER Code 121 indicates TP sensor rotational setting may be out of self-test range. Possible causes for this fault are:

Binding throttle linkage.
TP sensor not seated correctly.
Faulty TP sensor.
Faulty Powertrain Control Module (PCM).

Perform KOER SELF-TEST. Check for Code 327. If Code 327 is present with Code 121, service Code 327 and repeat QUICK TEST. If Code 327 is not present with Code 121, go to next step.

2) KOEO & KOER Code 121: Check For Binding Throttle Plate Inspect throttle body for binding. If throttle body is binding, check for binding throttle or cruise control linkage, vacuum line or harness interference. Repair as necessary and repeat QUICK TEST. If no mechanical problem is found, go to next step.

3) KOEO & KOER Code 121 & KOEO Code 123: Attempt To Generate Code 122 Code 123 indicates TP sensor signal is more than self-test maximum value. Possible causes for this fault are:

TP sensor not seated properly.
Faulty TP sensor.
Short circuit to power.
Faulty PCM.

Turn ignition off. Disconnect TP sensor. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Repeat KOEO SELF-TEST. Disregard all other codes at this time. If Code 122 is not displayed, go to step 5). If Code 122 is displayed, go to next step.

4) Check VREF Circuit Voltage Turn ignition on. Measure voltage between VREF and SIG RTN terminals at TP sensor wiring harness connector. If reading is 4-6 volts, replace TP sensor and repeat QUICK TEST. If reading is not 4-6 volts, reconnect TP sensor and go to TEST C.

5) Check TP Circuit For Short To Power Turn ignition off. Disconnect TP sensor. Disconnect PCM 60-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Install Breakout Box (49-UN01-058), leaving PCM disconnected. Measure resistance between test pin No. 47 and test pins No. 26 and 57 at breakout box. If any resistance is less than 10,000 ohms, repair short circuit in wiring harness. Remove breakout box, reconnect all components and repeat QUICK TEST. If both resistances are 10,000 ohms or more, replace PCM. Remove breakout box, reconnect all components and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 5) to step 10). No test procedures have been omitted.

10) KOEO Code 122: Attempt To Generate Code 123 Or 121 Code 122 indicates TP signal is less than minimum self-test value. Possible causes for this fault are:

TP sensor not seated correctly.
Faulty TP sensor.
Open circuit in wiring harness.
Grounded circuit in wiring harness.
Faulty PCM.

Turn ignition off. Disconnect TP sensor. Connect a jumper wire between VREF and TP terminals at TP sensor wiring harness connector. Perform KOEO SELF-TEST. If no codes are generated, remove jumper wire and go to step 13). If Codes 123 and 121 are not present, remove jumper wire and go to next step. If either Code 123 or 121 is displayed, replace TP sensor and repeat QUICK TEST.

11) Check VREF Circuit Voltage Turn ignition off. Disconnect TP sensor. Turn ignition on. Measure voltage between VREF and SIG RTN terminals at TP sensor wiring harness connector. If voltage is not 4-6 volts, turn ignition off. Reconnect all components and go to TEST C. If voltage is 4-6 volts, go to next step.

12) Check TP Sensor Circuit Continuity Turn ignition off. Disconnect TP sensor. 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 resistance between TP terminal at TP sensor wiring harness connector and test pin No. 47 at breakout box. If resistance is 5 ohms or more, repair open circuit. Remove breakout box, reconnect all components and repeat QUICK TEST. If resistance is less than 5 ohms, go to next step.

13) Check TP Circuit For Shorts To Ground Turn ignition off. Disconnect TP sensor. Disconnect PCM 60-pin connector and inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. With breakout box installed and PCM disconnected, measure resistance between test pin No. 47 and test pins No. 40, 46 and 60 at breakout box. If any reading is less than 10,000 ohms, repair short circuit. Remove breakout box, reconnect all components and repeat QUICK TEST. If all readings are 10,000 ohms or more, replace PCM. Remove breakout box, reconnect all components and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 13) to step 90). No test procedures have been omitted.

90) Continuous Memory Code 123 This test monitors TP sensor under simulated road conditions. Enter wiggle test. See CONTINUOUS MONITOR MODE (WIGGLE TEST) under QUICK TEST. Connect DVOM or diagnostic tester to STO terminal of Data Link Connector (DLC). While slowly opening throttle to WOT, observe DVOM or diagnostic tester for indication of fault. Slowly bring throttle to closed position. Lightly tap TP sensor and wiggle harness connector. This test checks for open or short in TP sensor and wiring harness. If no fault is indicated, go to step 92). If fault is indicated, go to next step.

91) Measure TP Circuit Voltage While Exercising TP Sensor Turn ignition off. Disconnect PCM 60-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Install Breakout Box (49-UN01-058), leaving PCM connected. Stay in wiggle test (as in previous step). Connect DVOM between test pins No. 47 and 46 at breakout box. Set DVOM on 20-volt scale. With ignition on and engine off, observe DVOM and repeat step 90). If fault occurs at less than 4.25 volts, inspect TP sensor connectors and terminals. If connectors and terminals are okay, replace TP sensor, clear codes and repeat QUICK TEST. If fault does not occur at less than 4.25 volts, TP sensor over-travel may have caused Continuous Memory Code 123. TP sensor is okay. Go to next step.

92) Check EEC-IV Wiring Harness While in wiggle test, bend and shake small sections of EEC-IV harness from TP sensor wiring harness connector to firewall and from firewall to PCM while observing analog voltmeter or scan tester. If fault is indicated, isolate fault in wiring and repair as necessary. Clear codes and repeat QUICK TEST. If no fault is indicated, go to next step.

93) Check PCM & Harness Connectors Turn ignition off. Disconnect PCM 60-pin connector from breakout box. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Clear codes from PCM memory and repeat QUICK TEST. If connectors and terminals are okay, fault cannot be duplicated at this time. Continuous Memory Code 123 testing is complete.

94) Continuous Memory Code 122: Monitor TP Circuit Under Simulated Road Shock Enter wiggle test. See CONTINUOUS MONITOR MODE (WIGGLE TEST) under QUICK TEST. Connect DVOM or diagnostic tester to STO terminal of Data Link Connector (DLC). Observe DVOM or diagnostic tester for indication of fault while performing the following:

Slowly open throttle to WOT.
Slowly bring throttle to closed position.
Lightly tap TP sensor and wiggle connector.

If fault is indicated, disconnect TP sensor. Inspect connectors and terminals. If connectors and terminals are okay, replace TP sensor. Clear codes from PCM memory and repeat QUICK TEST. If no fault is indicated, go to next step.

95) Check EEC-IV Wiring Harness Stay in wiggle test (as in previous step). Bend, wiggle and shake small sections of EEC-IV harness from TP sensor wiring harness connector to firewall and from firewall to PCM while observing analog voltmeter or scan tester. If fault is indicated, isolate fault in wiring and repair as necessary. Clear codes from PCM memory and repeat QUICK TEST. If no fault is indicated, go to next step.

96) Check PCM & Harness Connectors Turn ignition off. Disconnect PCM 60-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Clear codes from PCM memory and repeat QUICK TEST. If connectors and terminals are okay, fault cannot be duplicated at this time. Continuous Memory Code 122 testing is complete.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 96) to step 100). No test procedures have been omitted.

100) Continuous Memory Code 121: Throttle Position (TP) Sensor Integrity Code 121 indicates throttle position is inconsistent with MAF value. Turn ignition off. Disconnect PCM 60-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Install Breakout Box (49-UN01-058). Connect PCM to breakout box. Connect DVOM to test pins No. 46 and 47 at breakout box. Turn ignition on. Slowly apply throttle to WOT and release to closed position. Voltage should change smoothly from 0.4-4.5 volts. If voltage change is incorrect or erratic, ensure TP sensor is properly installed. If TP sensor is properly installed, replace TP sensor. Remove breakout box, reconnect all components and repeat QUICK TEST. If voltage change is okay, go to next step.

101) Check MAF Sensor Turn ignition off. Disconnect PCM 60-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Install Breakout Box (49-UN01-058). Connect PCM to breakout box. Start engine and warm it to normal operating temperature. Measure voltage between MAF sensor signal terminal and test pin No. 40 or 60 at breakout box. If voltage is not .6-.7 volts, replace MAF sensor. Remove breakout box, reconnect all components and repeat QUICK TEST. If voltage is .6-.7 volts, system is operating normally at this time. Sometime during the last 80 warm-up cycles, MAF sensor signal was out of range. However, EEC-IV system is now operating properly. Remove breakout box, reconnect all components and repeat QUICK TEST.