LEMON Manuals: Even more car manuals for everyone
Home >> Mazda >> 1994 >> B2300 SE, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> Circuit Test H - Fuel Control >> Diagnostic Aids

Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedures.

Fuel-contaminated engine oil may affect Codes 172, 136, 173 and 137. If fuel-contaminated engine oil is suspected, remove PCV valve from valve cover and repeat QUICK TEST. If problem is corrected, change engine oil and filter.

Only use this test to diagnose following.

To prevent replacement of good components, be aware following non-EEC areas may be cause of driveability concerns.

INDIVIDUAL INJECTOR RESISTANCE (1)

Engine Ohms
B2300 & B3000 11-18
(1) Resistance values are for a single injector.
MFI INJECTOR BANK RESISTANCE

Engine Ohms
2.3L 6.0-8.5
CIRCUIT TEST H ACRONYMS

Acronym Definition
HO2S Heated Oxygen Sensor
MFI (1) Multiport Fuel Injection
SFI Sequential Fuel Injection
(1) Used on 2.3L (except California).
FUEL PRESSURE SPECIFICATIONS (1)

Engine KOER: psi (kPa) KOEO: psi (kPa)
3.0L 30-45 (210-310) 35-45 (240-310)
2.3L 45-60 (310-415) 50-60 (345-415)
(1) Volume is 1 Pt. (.5L) in 30 Seconds.
Fig 1: Test Schematic (H1 - 2.3L Calif)
G94A65318
Fig 2: Test Schematic (H2 - 2.3L Except Calif)
G93D76102
Fig 3: Test Schematic (H3 - 3.0L)
G94C44836

1) Check For Contaminated Engine Oil  Turn ignition off. Remove PCV valve from valve cover. Inspect PCV system for damage. Inspect valve for blockage and movement of valve plunger. Repair as necessary. Perform KOEO SELF-TEST and KOER SELF-TEST. Service ignition Continuous Memory Code (if present) before KOER codes. If vehicle is a no-start, KOER Code 136, 137, 172, 173 or Continuous Memory Code 139, 144, 171, 175, 176 or 177 is set, install PCV valve and go to next step. If no codes are set, change engine oil and filter. Install PCV valve, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

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. If vehicle will not start, cycle ignition on and off several times. Check fuel pressure. See FUEL PRESSURE SPECIFICATIONS table. If fuel pressure is within specification, go to next step. If pressure is not within specification, go to FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article in the ENGINE PERFORMANCE section.

3) Check System Ability To Hold Fuel Pressure  Turn ignition on. Check fuel system for leaks. Repair or replace as necessary. If fuel system does not leak and pressure remains at specification for 60 seconds, go to next step (no-starts), step 5) (MFI) or step 6) (SFI).

4) Fuel Delivery Test  Release fuel system pressure. With fuel pressure gauge installed, pressurize fuel system as in step 1). Disconnect inertia switch. Crank engine 5 seconds. If fuel pressure drop is greater than 5 psi after 5 seconds of cranking, EEC-IV system is not causing no-start condition. Check additional no-start tests in TESTS W/O CODES article in the ENGINE PERFORMANCE section. If fuel pressure drop is less than 5 psi, remove fuel pressure gauge. Connect inertia switch. Go to step 7) for MFI or step 8) for SFI.

5) Cylinder Balance Test (MFI)  Connect a tachometer to engine. Start and run engine at idle. Disconnect and reconnect injectors individually, noting RPM drop as each injector is disconnected. IAC motor will attempt to re-establish RPM. If each injector does not produce a momentary drop in RPM, go to step 7). If each injector produces a momentary drop in RPM, go to step 13) for Code 136, 172 or 176, step 24) for Code 137, 173 or 177, or step 14) for all others.

CAUTION: If Continuous Memory Code 214 is present, repair as necessary before continuing with this test.

6) Cylinder Balance Test (SFI)  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. To interpret codes retrieved from test, refer to CYLINDER BALANCE TEST SERVICE CODES table. If cylinder balance fault codes are present, go to step 8). If Code 136, 172 or 176 is present, go to step 13). If Code 137, 173 or 177 is present, go to step 24). If any other codes are present, go to step 14).

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
50 Cylinder No. 5
60 Cylinder No. 6
70 Cylinder No. 7
80 Cylinder No. 8
538 (1) Retest
(1) Code 538 indicates throttle was touched when test was ran and test is not completed. Code 538 could also be output if Continuous Memory Code 214 is present.

7) Check Injector & Harness Resistance (MFI)  Turn ignition off. Disconnect PCM 60-pin connector. Inspect pins for damage. Install Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance of injector bank No. 1 between test pins No. 37 and 58 at breakout box. Measure resistance of injector bank No. 2 between test pins No. 37 and 59 at breakout box. Record resistances. See MFI INJECTOR BANK RESISTANCE table in this circuit test. If each resistance is within specification, go to step 12). If resistance is not as specified, repair open circuit on VPWR circuit for no-start or go to step 9) for all other conditions.

8) Check Injector & Harness Resistance (SFI)  Turn ignition off. Disconnect PCM 60-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure and record resistance between suspected injector circuit test pin and test pin No. 37. For no-start, measure and record resistance between injector circuit test pin and test pin No. 37. Refer to INDIVIDUAL INJECTOR RESISTANCE table in this circuit test. If each resistance is within specification, go to step 12). If resistance is not as specified, repair open circuit on VPWR circuit for no-start or go to next step for all other conditions.

9) Check Continuity Of Fuel Injector Harness  Turn ignition off. Disconnect injector wiring harness connector at injectors. Set DVOM on ohm scale. Measure resistance between test pins No. 37 and 57 at breakout box and each injector VPWR terminal at wiring harness connector. See Fig 1-29. Measure resistance between injector test pin(s) at breakout box and same injector circuit terminal at each injector wiring harness connector. If each resistance is less than 5 ohms, go to next step. If any resistance 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.

10) Check Injector Harness Circuit For Short To Power Or Ground  Turn ignition off and wait 10 seconds. With breakout box installed and PCM disconnected, disconnect fuel injector wiring harness connector. Measure resistance between injector test pin(s) and test pins No. 37, 40, 46, 57 and 60. 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 (SFI models) or go to next step (MFI models). If any resistance is less than 10,000 ohms, repair short. Remove breakout box, reconnect all components and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

11) Isolate Faulty Injector Circuit  Turn ignition off. leave Install breakout box, and disconnect PCM. Disconnect all injectors on suspect bank. With DVOM set on ohm scale, connect one injector and measure resistance between test pins No. 37 and 58 (injector bank No. 1) or 59 (injector bank No. 2). Disconnect injector, and repeat process for all other injectors. See INDIVIDUAL INJECTOR RESISTANCE table. If all injectors are within specification, go to next step. If injectors are not as specified, replace injector. Remove breakout box, and reconnect components. Drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

12) Check Injector Drive Signal  With ignition off and breakout box installed, connect PCM to breakout box. Use a non-powered 12-volt test light, and connect as follows:

Crank or start engine. If test light glows dimly, system is operating correctly. Clean injectors, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST and CYLINDER BALANCE TEST. If test light does not glow dimly (no light/bright light), replace PCM. Reconnect all components. Drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

13) Check Thermactor Operation  If vehicle is equipped with pulse-air or does not have secondary air injection system, go to next step. A HO2S which is always lean could be caused by thermactor air being diverted upstream from HO2S. With dual HO2S, Code 172 applies to right or rear HO2S, and Code 136 or 176 applies to left or front HO2S. Turn ignition off. Disconnect secondary air hose(s) from pump and vent to atmosphere. Perform KOER SELF-TEST. If Code 172, 136 or 176 is present, reconnect air hose(s) and go next step. If Continuous Memory Code 139, 144, 171, 176 or 177 is present, go to step 90). If code(s) is not present, repair air injection system as necessary.

14) Check HO2S Integrity  A HO2S which is always lean, slow to switch or does not switch could be caused by following.

Turn ignition off. Inspect HO2S wiring harness for damage. Inspect HO2S and connector for signs of fluid entry. Repair or replace as necessary. Start and run engine at 2000 RPM for 2 minutes. Turn ignition off. Run KOER SELF-TEST. If fault codes are present, go to next step (MAP sensor-equipped models) or step 16) (MAF sensor-equipped models). If no code is present, go to step 21).

15) Check HO2S (Engines With MAP Sensors)  Vacuum or air leaks in non-EEC-IV areas could cause Code 172, 136 or 176. Check following possibilities before continuing.

Turn ignition off. Ensure MAP sensor output voltage is correct. See CIRCUIT TEST DF, step 3). Disconnect appropriate HO2S from wiring harness connector. On 3-wire HO2S, connect DVOM to HO2S terminal at sensor wiring harness connector and negative battery terminal. On 4-wire HO2S, connect DVOM to HO2S and HO2S GND or SIG RTN terminal at sensor wiring harness connector. On all models, disconnect and plug vacuum line at MAP sensor. Start engine and apply 10-14 in. Hg to MAP sensor. Run engine at 2000 RPM for 2 minutes. If reading is 0.5 volt or more, go to step 17). If reading is less than 0.5 volt, replace HO2S and repeat QUICK TEST.

16) Check HO2S  Purpose of this test is to verify HO2S can generate a voltage signal of greater than 0.5 volt during KOER SELF-TEST. Vacuum or air leaks in non-EEC-IV areas could cause Code 172, 136 or 176. Check following possibilities before continuing.

Turn ignition off. Disconnect appropriate HO2S from harness. On 3-wire HO2S, connect DVOM to HO2S terminal at sensor wiring harness connector and negative battery terminal. On 4-wire HO2S, connect DVOM between HO2S terminal and HO2S GND or HO2S GND terminal at HO2S wiring harness connector. On all models, run engine at 2000 RPM for 2 minutes. Repeat KOER SELF-TEST and monitor HO2S voltage. If voltage is 0.5 volt or more at end of self-test, go to next step. If voltage is less than 0.5 volt, replace HO2S and repeat QUICK TEST.

17) Check Continuity Of HO2S Ground Circuits  Turn ignition off. Install breakout box, leaving PCM disconnected. Disconnect suspect HO2S wiring harness connector. Inspect connector for damage, moisture and corrosion. Repair as necessary. Measure resistance between HO2S test pin at breakout box and HO2S terminal at sensor wiring harness connector. On 3-wire HO2S, measure resistance between HO2S GND test pin at breakout box and negative battery terminal. On 4-wire HO2S, measure resistance between SIG RTN test pin at breakout box and SIG RTN terminal at sensor wiring harness connector. Where applicable, measure resistance between HO2S GND and SIG RTN at breakout box. On all models, go to next step if each resistance is less than 5 ohms. If any resistance is 5 ohms or more, repair open circuit. Remove breakout box, and reconnect all components. Drive vehicle for 5 minutes at 55 MPH. Repeat QUICK TEST.

18) Check HO2S Circuit For Short To Ground  Turn ignition off. Leave breakout box installed and PCM disconnected. Disconnect HO2S. Measure resistance between HO2S circuit test pin and test pins No. 40, 46 and 49 at breakout box. If any reading is less than 10,000 ohms, repair short to ground. Drive vehicle at 55 MPH for 5 minutes and repeat QUICK TEST. If reading is 10,000 ohms or more, go to next step.

19) Check HO2S For Short To Ground  Ensure ignition is off and PCM is disconnected. With HO2S disconnected, measure resistance between PWR GND and HO2S terminal at HO2S connector. On 4-wire HO2S, also measure resistance between HO2S GND and/or SIG RTN terminal at sensor wiring harness connector. If resistance is less than 10,000 ohms, replace HO2S. Drive vehicle for 5 miles at 55 MPH and repeat QUICK TEST. If resistance is 10,000 ohms or more, perform following procedure as applicable.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 19) to step 21). No test procedures have been omitted.

21) Check Resistance Of HO2S Heating Element  Turn ignition off. Disconnect suspect HO2S. Inspect both ends of connector for damage, moisture and corrosion. Repair if necessary. Measure resistance between IGNITION RUN circuit and PWR GND circuit at HO2S connector. Hot-to-warm engine resistance should be 5-30 ohms. Cold engine resistance is 2-5 ohms. If resistance is within specification, go to next step. If resistance is not as specified, replace HO2S and repeat QUICK TEST.

22) Check For Power At HO2S Harness Connector  Disconnect HO2S. Turn ignition on. Measure voltage between IGNITION RUN and PWR GND circuits at HO2S wiring harness connector. If voltage is less than 10.5 volts, go to next step. If voltage is 10.5 volts or more, HO2S system and fuel delivery are okay. HO2S may have cooled before KOER SELF-TEST. If driveability symptom continues, fault is in area common to all cylinders. See TESTS W/O CODES article in the ENGINE PERFORMANCE section.

23) Check Continuity Of Power Ground Circuit  Turn ignition off. Measure resistance between PWR GND circuit at HO2S wiring harness connector and negative battery terminal. If resistance is less than 5 ohms, repair open in IGNITION RUN circuit and repeat QUICK TEST. If resistance is 5 ohms or more, repair open in PWR GND circuit and repeat QUICK TEST.

24) Diagnostic Test Code 137, 173 Or 177: Check HO2S SIGNAL For Short To Power  On dual HO2S systems, Code 173 applies to right or rear sensor. Codes 137 and 177 apply to left or front sensor. HO2S continuously rich could be caused by following.

Turn ignition off. Disconnect appropriate HO2S. Inspect connector for damage and repair as necessary. Turn ignition on. Measure voltage between HO2S and PWR GND terminal at HO2S wiring harness connector. If reading is less than 0.5 volt, go to step 26). If reading is 0.5 volt or more, go to next step.

25) Check For Short To Power  Turn ignition off. Disconnect HO2S. Inspect wiring harness for damage and repair as necessary. Disconnect PCM 60-pin connector. Install Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Disconnect suspect HO2S. Measure resistance between VPWR test pin and HO2S SIG test pin at breakout box. If reading is 10,000 ohms or more, replace PCM. Remove breakout box, and reconnect all components. Drive vehicle 5 miles at 55 MPH. Repeat QUICK TEST. If reading is less than 10,000 ohms, repair short circuit. Remove breakout box, and reconnect all components. Drive vehicle 5 miles at 55 MPH. Repeat QUICK TEST.

26) Check HO2S For Short To IGNITION RUN Circuit  Turn ignition off. Disconnect HO2S. Measure resistance between IGNITION RUN terminal and HO2S terminal at HO2S wiring harness connector. If resistance is 10,000 ohms or more, go to next step for Codes 173, 137 and 177, step 28) for Codes 171, 174 and 175, or step 30) on models with MAF sensor. If resistance is less than 10,000 ohms, replace HO2S. Drive vehicle for 5 miles at 55 MPH, and repeat QUICK TEST.

27) Attempt To Generate Code 172, 136 Or 176  Turn ignition off. Disconnect appropriate HO2S. Using jumper wire, connect HO2S terminal at HO2S wiring harness connector to negative battery terminal. Repeat KOER SELF-TEST. If Code 172, 136 or 176 is present, remove jumper wire and go to next step. If Codes 172, 136 and 176 are not present, remove jumper wire. Disconnect PCM connector and inspect for damage. If connector is okay, replace PCM. Drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 27) to step 30). No test procedures have been omitted.

30) HO2S Check  Turn ignition off. Disconnect HO2S. For 4-wire HO2S, connect DVOM to HO2S terminal and HO2S GND or SIG RTN terminal at HO2S connector. For 3-wire HO2S, connect DVOM to HO2S terminal at HO2S connector and negative battery terminal. On all models, create vacuum leak to force HO2S to go lean. Remove PCV valve hose. Start engine. Raise engine speed to about 2000 RPM. DVOM should indicate less than 0.4 volt within 30 seconds. If voltage is not as specified, replace HO2S. Reconnect vacuum hoses, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST. If voltage is as specified, go to step 90).

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 30) to step 90). No test procedures have been omitted.

90) Check Continuous Monitor Mode  Start and warm engine to normal operating temperature. Raise engine speed to 2000 RPM for 2 minutes and then return to idle. Enter KOER wiggle test. See CONTINUOUS MONITOR MODE (WIGGLE TEST) under QUICK TEST. While observing DVOM or scan tester, shake or bend small sections of wiring harness from HO2S to PCM. Wiggle, shake or bend small sections of wiring harness from HO2S GND to PCM. If no fault is indicated, remain in CONTINUOUS MONITOR MODE and go to next step. If fault is indicated, isolate and repair fault as necessary. Clear codes. Repeat QUICK TEST.

91) Continuous Monitor Test Drive Check  While still in KOER wiggle test, test drive vehicle for 5 miles at 55 MPH over smooth roads. Drive an additional 5 miles at 55 MPH over rough roads. If possible, drive vehicle through a pool of water to wet HO2S and connector. If fault is indicated, isolate fault and repair as necessary. Clear codes, and remove breakout box. Repeat QUICK TEST. If no codes are indicated, exit KOER wiggle test and go to next step.

92) Check HO2S Switching  Turn ignition off. Inspect wiring harness for proper routing and insulation. Check for burnt, chaffed or open wires. Repair as necessary. Disconnect PCM 60-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install breakout box. Connect PCM to breakout box. Connect analog voltmeter to suspect HO2S test pin and HO2S GND at breakout box. Test drive vehicle for 5 miles at 55 MPH while observing voltmeter. HO2S should switch from .3 volt to .9 volt within 3 seconds. If HO2S does not switch as described, replace HO2S. Connect all components, and repeat QUICK TEST. If HO2S switches as described, fault cannot be identified or duplicated at this time. See INTERMITTENTS in TESTS W/O CODES article in the ENGINE PERFORMANCE section.

scientia non olet · About LEMON Manuals