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Circuit Test D2

Perform this test only when Codes 12, 13, 16, 17, 19, 23, 38, 53, 58, 63, 68, 71, 73, or 93 are displayed or when directed here by DIAGNOSIS BY SYMPTOM TEST. To prevent replacement of good components be aware that the following non-EEC related areas may be at fault: throttle stop screw out of adjustment, vacuum leaks, sticking throttle, or basic engine (valves, timing, etc.).

Fig 1: DC Motor/Idle Tracking Switch (ITS) & TPS Circuit (1 of 2)
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Fig 2: DC Motor/Idle Tracking Switch (ITS) & TPS Circuit (2 of 2)
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Fig 3: DC Motor Shaft Measurements
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  1. Code 13: Checking DC Motor Operation. Code 13 indicates and error in idle speed control management. Engine did not return to a specified lower RPM prior to "Goose" test portion of Self-Test. Possible causes for this fault are; faulty DC motor, open or shorted ISC circuit, faulty ECA. Turn key off and wait 10 seconds. Disconnect harness from DC motor. Using jumper wires, connect ISC positive (+) circuit of DC motor to battery positive (+) terminal and ISC negative (-) circuit of DC motor to battery negative terminal for 4 seconds. DC motor shaft should extend more than 2" (50 mm). See DC MOTOR SHAFT MEASUREMENTS illustration. Now connect ISC + circuit of DC motor to battery negative terminal and ISC- circuit of DC motor to battery positive terminal for 4 seconds. DC motor shaft should retract to less than 1 3/4" (44 mm). If DC motor shaft moves in and out as indicated, go to next step. If not, replace DC motor and repeat QUICK TEST.
  2. Checking Continuity of ISC+ and ISC- Circuits. Turn key off and wait 10 seconds. Leave harness disconnected from DC motor. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Connect breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance between test pin No. 41 and ISC- circuit at harness connector and between test pin No. 21 and ISC+ circuit at harness connector. If both readings are less than 5 ohms, go to next step. If readings are 5 ohms or more, repair circuit(s) and repeat QUICK TEST.
  3. Checking ISC+ and ISC- Circuits For Shorts To Ground. Turn key off and wait 10 seconds. Leave breakout box and ECA disconnected. Set DVOM on 200K-ohm scale. Measure resistance between test pin No. 41 and test pins No. 40, 46 and 60. Also measure resistance between test pin No. 21 and test pins No. 40, 46 and 60. If all readings are greater than 10K ohms, go to next step. If any reading is less than 10K ohms, repair faulty circuit(s) and repeat QUICK TEST.
  4. Checking ISC+ and ISC- For Shorts to PWR. Turn key off and wait 10 seconds. Leave breakout box installed and ECA disconnected. Disconnect DC motor from harness. Set DVOM to 20 volt scale. Measure voltage between test pin No. 41 and test pins No. 40 and 60. Also measure voltage between test pin No. 21 and test pins No. 40 and 60. If all readings are less than one volt, replace ECA and repeat QUICK TEST. If any reading is more than one volt, repair faulty circuit(s) and repeat QUICK TEST.
  5. Code 58: Check For Full Motor Retraction. Turn key off and wait 10 seconds. Disconnect DC motor from harness. Using jumper wires, connect DC motor ISC - circuit to battery positive (+) terminal and ISC positive (+) circuit to battery negative (-) terminal for 4 seconds. DC motor shaft should be fully retracted, away from throttle lever. If shaft is retracted, go to step 7). If shaft does not retract, go to next step.
  6. Measuring Motor Retraction. Turn key off and wait 10 seconds. Disconnect DC motor from harness. Ensure DC motor is fully retracted. Measure distance from DC motor mounting bracket to tip of motor shaft. See DC MOTOR SHAFT MEASUREMENTS. If DC motor shaft is retracted to less than 1 3/4" (44 mm), reconnect DC motor. Check throttle stop adjustment. If DC motor shaft does not retract, replace DC motor and repeat quick test.
  7. Checking Idle Tracking Switch (ITS). Turn key off and wait 10 seconds. Disconnect DC motor from harness. Ensure DC motor is fully retracted and not touching throttle lever. Set DVOM on 200-ohm scale. Measure resistance between ITS circuit and SIG RTN at DC motor connector. If reading is less than 5 ohms, go to next step. If not, replace DC motor and repeat QUICK TEST.
  8. Checking Continuity of ITS & SIG RTN Circuits. Turn key off and wait 10 seconds. Disconnect DC motor from harness. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Connect breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance between test pin No. 46 and SIG RTN circuit at DC motor harness connector. Also measure resistance between test pin No. 28 at the breakout box and ITS circuit at DC motor harness connector. If both readings are less than 5 ohms, reconnect DC motor. Replace ECA and repeat QUICK TEST. If any reading is 5 ohms or more, reconnect DC motor. Repair open circuit(s) and repeat QUICK TEST.
  9. Code 68: Checking Idle Tracking Switch. Code 68 indicates DC motor shaft is in contact with throttle lever when DC motor signal was produced to retract shaft. Possible causes for this fault are: faulty DC motor, short to ground in ITS circuit or faulty ECA. Turn key off and wait 10 seconds. Disconnect DC motor from harness. Set DVOM on 200-ohm scale. Measure resistance between ITS circuit and SIG RTN circuit at DC motor connector. If all readings are greater than 5 ohms, go to next step. If any reading is 5 ohms or less, replace DC motor and repeat QUICK TEST.
  10. Checking ITS For Shorts To Ground. Turn key off and wait 10 seconds. Disconnect DC motor from harness. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Connect breakout box, leaving ECA disconnected. Set DVOM on 200K-ohm scale. Measure resistance between test pin No. 28 and test pins No. 40, 46, and 60. If all readings are greater than 10K ohms, reconnect DC motor. Replace ECA and repeat QUICK TEST. If any reading is 10K ohms or less, reconnect DC motor. Repair faulty circuit(s) and repeat QUICK TEST.
  11. Code 93: Checking Throttle Linkage. Code 93 indicates a fault between DC motor a throttle linkage. Turn key off and wait 10 seconds. Inspect throttle for freedom of movement to wide open throttle and for damaged or bent throttle lever. If throttle lever and linkage are okay, replace DC motor and repeat QUICK TEST. If throttle lever and/or linkage are damaged, repair as necessary and repeat QUICK TEST.
  12. Code 23: Checking Throttle Plate Closing. Code 23 indicates throttle plate is not in correct position during Self-Test. Possible causes for this fault are: a faulty TPS, open in TPS circuit, or a faulty ECA. Perform KOEO SELF-TEST. Disconnect DC motor when shaft is fully retracted. Turn key off and wait 10 seconds. Remove air cleaner from throttle body. Inspect throttle for freedom of movement and for proper closing of throttle valves. If throttle moves freely and closes without obstructions, reconnect DC motor and go to next step. If throttle binds or does not close properly, repair as necessary and repeat QUICK TEST.
  13. Checking Voltage Of VREF to SIG RTN. Turn key off and wait 10 seconds. Disconnect TPS harness connector at throttle body. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Set DVOM on 20-volt scale. Turn key on, leaving engine off. Measure voltage between VREF and SIG RTN at TPS harness connector. If reading is between 4-6 volts, reconnect TPS and go to next step. If reading is incorrect, go to CIRCUIT TEST A3 , step 1).
  14. Checking Throttle Stop RPM. Perform KOEO SELF-TEST. Disconnect DC motor after shaft has fully retracted and exit SELF-TEST. Start engine and verify that throttle stop RPM is less than curb idle speed. If throttle stop RPM is set to less than curb idle speed, replace TPS. Connect DC motor and repeat QUICK TEST. If throttle stop RPM is not less than curb idle speed, adjust throttle stop RPM. Connect DC motor and repeat QUICK TEST.
  15. Code 53: Generate Code 63. Code 53 indicates TPS output signal is greater than the Self-Test maximum of 4.7 volts. Possible causes for this fault are: faulty TPS, faulty ECA or short to power in TPS circuit. Turn key off and wait 10 seconds. Disconnect harness from TPS at throttle body. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Perform KOEO SELF-TEST and record codes. If Code 63 is displayed, go to next step. If Code 63 is not displayed, go to step 17). Ignore all other codes.
  16. Check Voltage at VREF to SIG RTN. Turn key off and wait 10 seconds. Disconnect TPS harness at throttle body. Set DVOM on 20 volt scale. Turn key on, leaving engine off. Measure voltage between VREF and SIG RTN at TPS harness connector. If reading is 4-6 volts, replace TPS and repeat QUICK TEST. If not, go to CIRCUIT TEST A3 , step 1).
  17. Check TP Signal For Short To Power. Turn key off and wait 10 seconds. Disconnect TPS harness at throttle body. Set DVOM on 200K ohm scale. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Install breakout box, leaving ECA disconnected. Measure resistance between test pin No. 47 and test pins No. 26 and 57 at breakout box. If both readings are 10K ohms or greater, replace ECA and repeat QUICK TEST. If any reading is less than 10K ohms, repair faulty circuit(s) and repeat QUICK TEST.
  18. Code 63: Generate Service Code 53. Code 63 indicates TP signal is less than Self-Test minimum of 0.2 volt. A failure mode signal indicates a closed throttle to the ECA. Possible causes for this fault are: a faulty TPS or ECA, open in TPS circuit or short to ground in TPS. Turn key off and wait 10 seconds. Disconnect TPS harness at throttle body. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Using jumper wire, connect VREF to TP signal at TPS harness connector. Perform KOEO SELF-TEST. If no codes are displayed, immediately remove jumper wire and go directly to step 21). If Code 53 is displayed, replace TPS sensor and repeat QUICK TEST. If Code 53 is not displayed, go to next step. Ignore all other codes at this time.
  19. Voltage Check: VREF to SIG RTN. Turn key off and wait 10 seconds. Disconnect TPS harness at throttle body. Set DVOM on 20-volt scale. Turn key on, leaving engine off. Measure voltage between VREF and SIG RTN at TPS harness connector. If reading is between 4-6 volts, go to next step. If not, go to CIRCUIT TEST A3 , step 1).
  20. Checking Continuity of TP Signal Circuit. Turn key off and wait 10 seconds. Disconnect TPS harness at throttle body. Set DVOM on 200-ohm scale. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Install breakout box, leaving ECA disconnected. Measure resistance between TPS signal at harness connector and test pin No. 47 at breakout box. If reading is less than 5 ohms, go to next step. If not, repair circuit. Reconnect TPS harness and repeat QUICK TEST.
  21. Checking TP Signal For Short To Ground. Turn key off and wait 10 seconds. Disconnect TPS harness at throttle body. With breakout box installed and ECA disconnected, set DVOM on 200K-ohm scale. Measure resistance between TP signal at harness connector and test pins No. 40, 46, and 60 at breakout box. If all readings are greater than 10K ohms, replace ECA. Connect TPS and repeat QUICK TEST. If any reading is less than 10K ohms, repair faulty circuit(s) and repeat QUICK TEST.
  22. Code 73: Displayed. Code 73 indicates ECA did not detect sufficient change in throttle position during "Goose" test. Possible causes for this fault are: faulty TPS or sensor circuit, faulty EGR system, faulty EGO sensor or sensor circuit or faulty ITS circuit. Perform KOEO SELF-TEST. If Code 73 is still displayed in KOEO SELF-TEST, replace TPS and repeat QUICK TEST. If Code 73 is not displayed, repair other codes.
  23. Code 12: Check For Codes That Could Cause Code 12. Code 12 indicates system is not capable of raising engine speed above curb idle. Perform KOER SELF-TEST. If Codes 31, 32, 34, 35, 41, or 58 are displayed, repair these codes first. See KOER SELF-TEST table for instructions. If these codes are not displayed, go to next step.
  24. Check For Sticking Throttle Linkage. Check throttle plates and linkage for binding. Check cruise control linkage for proper adjustment. If throttle opens and closes properly, go to next step. If throttle does not operate properly, repair throttle as required and repeat QUICK TEST.
  25. Checking DC Motor Operation. Turn key off and wait 10 seconds. Disconnect harness from DC motor. Ensure other pins are not shorted when connecting jumper to ISC connector. Using jumper wires, carefully connect ISC positive (+) circuit of DC motor to battery positive (+) terminal and ISC negative (-) circuit of DC motor to battery negative terminal for 4 seconds. DC motor shaft should extend more than 2" (50 mm). See DC MOTOR SHAFT MEASUREMENTS illustration. Now connect ISC positive (+) circuit of DC motor to battery negative (-) terminal and ISC negative (-) circuit of DC motor to battery positive (+) terminal for 4 seconds. DC motor shaft should retract to less than 1 3/4" (44 mm). If DC motor shaft moves in and out as indicated, replace ECA and repeat QUICK TEST. If not, replace DC motor and repeat QUICK TEST.
  26. Code 13 or 19: Erratic Idle Check. Code 13 or 19 indicates that the engine does not remain at a specified lower RPM prior to entering the "Goose" test portion of the Self-Test. Possible causes for this fault are; faulty MAP/BP sensor, faulty EGR sensor or circuit, faulty EGO sensor or circuit, faulty ITS. Ensure engine is at normal operating temperature. Deactivate SELF-TEST. Ensure A/C is off (if equipped). Start and run engine for 3 minutes, alternating between 30 second idle and 5 second part throttle operation. If idle is erratic, go to next step. If idle is not erratic at end of 3 minute idle/part throttle test, go to step 28).
  27. Check For Additional Codes During KOER SELF-TEST. Check for vacuum leaks, and Codes 22, 31, 32, 34, 35, 41, or 58. Repair these codes before going on to next step.
  28. Checking Throttle Plates and Linkage. Inspect throttle plates and/or linkage for binding. If throttle opens and closes properly, replace DC motor and repeat QUICK TEST. If throttle binds, repair throttle as required and repeat QUICK TEST.
  29. Continuous Memory Code 99: Check ECA Operation. Code 99 indicates the ECA has not received enough information to control engine idle speed. Deactivate SELF-TEST and start engine. DO NOT  touch the throttle. Allow engine to idle for 2 minutes and shut engine off. When key has been off 10 seconds, run KOEO SELF-TEST. After service codes are displayed, deactivate SELF-TEST. Turn key off and wait 10 seconds. Rerun KOER SELF-TEST. If Code 99 is displayed, replace ECA. If Code 99 is not displayed, service other service codes.
  30. Code 16 or 17: Related Mechanical Problems. Code 16 may indicate that the accelerator pedal was touched during KOER SELF-TEST. Code 17 indicates an electrical load such as as engine cooling fan or A/C compressor was activated during the SELF-TEST. Check engine for vacuum leaks, binding throttle linkage, base ignition timing, and throttle stop screw adjustment. If these items are okay, service other codes as necessary and rerun QUICK TEST. If a faulty item is found, service as necessary and rerun QUICK TEST.
  31. Continuous Code 13 Displayed. Code 13 indicates that in the last 40 engine warm-up cycles, the Throttle Position Sensor (TPS) rotation did not follow the reaction of DC motor when idle speed control was in dashpot mode. This condition may be caused by the following:
    • DC motor sticking at part throttle.
    • An open in ITS circuit which, when coupled with other inputs to ECA, causes EEC system to falsely enter dashpot mode.
    • TPS sticking at part throttle.

    Each of these areas may generate KOEO SELF-TEST Codes or Continuous Memory Codes. If repairs have been made for KOEO SELF-TEST Codes 13 or 58, Continuous Memory Code 13 can be considered serviced and erased from memory. If Continuous Memory Codes 13 and 38 are present, service Code 38 first. If these codes are not present, make the following checks:

    • Go to step 1) of this test and check for FULL travel of DC motor shaft. Replace DC motor if travel is not obtained. Leave motor in FULL retract position. See DC MOTOR SHAFT MEASUREMENTS illustration.
    • With motor in full retract position, and with ITS not touching throttle lever check for an open in ITS circuit. Turn key off and install breakout box. Make necessary connector/pin inspections. With DVOM on 200-ohm scale, monitor resistance between test pins No. 28 and 46 while tapping, wiggling, and bending DC motor connector and harness. DO NOT  push in idle tracking switch. If DVOM reading changes from less than 5 ohms to more than 5 ohms, an open circuit exists in wiring. Repair as necessary.
    • Check for binding TPS by monitoring TPS voltage while moving throttle from a wide open position to a closed throttle position. Install breakout box and make all necessary connector/pin inspections. Fully retract DC motor shaft by placing a jumper wire between test pins No. 41 and 57. When motor is fully retracted, disconnect it at harness and remove jumper wire from breakout box. Turn key on and set DVOM on 20-volt scale. Slowly move throttle to wide open and closed throttle positions. Readings should move from more than 4 volts to less than 1.5 volts. If voltage readings hang up in mid-range, showing zero to 1.5 volts, replace TPS. If readings are correct, TPS is okay, do not service.

  32. Continuous Code 38 Displayed. Code 38 indicates that in the last 40 engine warm-up cycles the idle tracking switch was open (ITS touching throttle) when throttle angle was greater than the maximum extension of DC motor shaft. This condition could be caused by the following conditions:
    • An open in ITS circuit.
    • Idle tracking switch stuck in open (pushed in) position.

    These conditions may cause a Code 58 to appear in KOEO SELF-TEST. If repair has been made for Code 58, Continuous Memory Code 38 can be considered serviced, and erased from memory. If KOEO SELF-TEST Code 58 was not displayed, check the following:

    • With DC motor fully retracted and ITS not touching throttle lever, check for an intermittent in ITS circuit. Turn ignition off and install breakout box. Make the necessary connector/pin inspections. With DVOM on 200-ohm scale, measure resistance between test pins No. 28 and 46 while tapping, wiggling, or bending DC motor connector and harness. DO NOT  push in idle tracking switch. If DVOM reading changes from less than 5 ohms to more than 5 ohms, an open circuit exists in wiring. Repair as necessary.

  33. Continuous Code 71 Displayed. This code indicates that in the last 40 engine warm-up cycles the idle tracking switch was closed (ITS not touching throttle lever) when DC motor was in preset position. This condition can be caused by the following:
    • ITS circuit shorted to ground or SIG RTN.
    • ITS stuck in closed position (NOT in pushed in position).

    Either of these conditions may cause KOEO SELF-TEST Code 68. If repairs have been made for Code 68, Continuous Memory Code 71 can be considered serviced and erased from memory. If Code 68 was not displayed, check the following:

    • Check ITS circuit for an intermittent short to ground or SIG RTN. Turn key off. Enter KOEO CONTINUOUS MONITOR (WIGGLE) TEST and systematically tap, wiggle, or bend harness while looking for indication of fault. If fault is created, repair as necessary. Due to nature of this test step, Code 71 will NOT reappear in memory if fault is found.

  34. Continuous Code 53 Displayed. Code 53 indicates TPS sensor output signal was greater than the 4.7 volt Self-Test maximum. The failure mode sends a WOT signal to the ECA. Possible causes for this fault are: faulty TPS or faulty ECA, short to power in TPS circuit. Using KOEO CONTINUOUS MONITOR (WIGGLE) TEST, observe VOM or diagnostic tester for indication of fault, while slowly moving throttle slowly to WOT. Slowly release throttle to closed position and lightly tap on TPS to simulate road shock and lightly wiggle TPS harness connector. If fault is indicated, go to next step. If not, go to step 36).
  35. Throttle Position Signal Voltage. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Install breakout box and connect ECA. Set DVOM on 20-volt scale. Connect DVOM from test pin No. 47 to test pin No. 46. Turn key on, leaving engine off. While observing DVOM, move throttle slowly to closed position and lightly tap on TPS. Wiggle TPS harness and connector. If fault occurs at less than 4.25 volts, disconnect and inspect connectors. If okay, replace TPS and repeat QUICK TEST. If fault occurs at greater than 4.25 volts, TPS overtravel may have caused Code 53. Go to next step.
  36. Checking EEC-IV Harness. Observe VOM or diagnostic tester for fault indication while grasping harness close to sensor connector. Wiggle, shake, or bend a small section of harness while working toward firewall. Repeat procedure from firewall to ECA. If fault is indicated, isolate fault and repair as necessary. After repairs repeat QUICK TEST. If no fault occurs, go to next step.
  37. Checking ECA and Harness Connectors. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect both connector and connector terminals for obvious fault or damage. If connector and terminals are okay, fault cannot be duplicated at this time. Testing is complete. If connector or terminals are damaged, repair as necessary. After repairs, repeat QUICK TEST.
  38. Checking Continuous Codes 23 or 63: Operate TPS. Code 23 or 63 indicates TPS output signal is less than the Self-Test minimum of 0.2 volt. Failure mode indicates closed throttle to the ECA. Possible causes for this fault are: faulty TPS, open or short to ground in TPS harness circuit or faulty ECA. Using KOEO CONTINUOUS MONITOR (WIGGLE) TEST, observe VOM or diagnostic tester for indication of fault while slowly moving throttle to WOT. Slowly release throttle to closed position, lightly tap on TPS to simulate road shock and lightly wiggle TPS harness connector. If fault is indicated, disconnect and inspect connectors. If connectors and terminals are okay, replace TPS and repeat QUICK TEST. If no fault is indicated, repeat test steps 36) and 37).
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