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No-Code Diagnosis

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  1. No-Code Diagnosis A Step-by-Step Guide to Success Jim Halderman

  2. Topics to Be Discussed • Where to start diagnosis? • Why following a procedure rather than just performing tests works best • How to look at scan tool data (PIDs) in a sequence order to reduce diagnostic time. • How to use fuel trim to diagnosis fuel delivery problems. • Many case studies as examples

  3. Where do you start? • Verify-If you can not verify the customer concern, you can not verify the repair • This is hard for some customers to understand. “ Don’t you believe me?” • Have the owner drive is instead of the technician • Is the troubleshooting procedure explained to the customer?

  4. Step #2 • Visual inspection • An older technician once told me that “the vehicle will tell you want is needed” • True?

  5. Turbo Ford Case Study(ran rough after cylinder head replacement)

  6. Checked Air Vane Sensor

  7. Verified the Cam Timing

  8. Verified Ignition Timing

  9. Checked the Valve Clearance

  10. Checked Injectors

  11. Tachometer fluctuated when running • What can cause that to happen? • Bad coil? • Poor connections on coil? • Bad ignition control module? • Bad tachometer? • Poor ground?

  12. Grounded Cylinder Head

  13. Ran OK with the Jumpers

  14. Turbo Ford Story Conclusion • Cylinder head was not properly grounded to the block • Sealant was used on the head bolt threads • The ground from the battery was connected to the block; not the head • Spark plugs need to be properly grounded • Poor ground caused feedback to the tachometer

  15. Step #3 • Check for diagnostic Trouble Codes (DTCs) • Could be performed before step #2 • Check for pending codes too • Check that all monitors have run • Could there be a driveability problem without a DTC? yes

  16. Monitors Continuous: Misfire, Fuel System, and Comprehensive Non-Continuous: Evap., EGR, O2 Sensors, O2 Sensor Heaters, Catalyst, Heated Catalyst, A/C System, Secondary Air, and Warm-ups NOTE: In emission areas, a specific number of monitors need to be “complete” or “ready” in order to perform an emissions test.

  17. Monitors vs. DTCs • If a monitor cannot run, then a DTC cannot be set • Always check to see if the all of the monitors have run and passed • Some require certain temperatures

  18. Step #4 • Check for any technical service bulletins (TSBs) • Why not use the resources of many before you? • I would also suggest using www.iatn.net • Identifix (free to NATEF certified programs)

  19. Step #5 • Check scan tool data • Look at the “high authority” sensor information

  20. Step #6 • Narrow the problem to a cylinder or system • The systems could be the fuel, ignition or emission control system • The cylinder could be just one cylinder or a bank of cylinders

  21. Step #7 • Find the root cause • The root cause may not be obvious but has to be found and repaired to prevent a comeback

  22. Step #8 • Verify the repair • Use the same conditions used to verify the problem to verify the repair • Clear DTCs (not if going to an emission test????) • Write the story on the work order • The three Cs (Complaint, Cause and Correction)

  23. Dash Warning Light On? • Check Engine • Check Engine Soon • Maintenance Required • Service Vehicle Soon • Air Bag • Side Air Bag • Trac

  24. P0304 Example

  25. EGR passage problem is shown.

  26. Remove upper plenum for EGR inspection.

  27. 5 out of 6 are stopped up!

  28. No-Code Diagnosis • Many times are tough to locate • Keep the basics in mind • The primary purpose of OBDII is emissions-not driveability!

  29. 2004 Prius Case Study • Poor fuel economy (25 mpg instead of normal 40+) • No codes • Scan data (PIDs) looked normal • Found right front disc brake caliper stuck. • No drop in performance noticed by the driver

  30. Rough Idle; Surge; No Codes

  31. Gear Wear!

  32. Gear /Pin / Washer Kit Available

  33. Plate spins on shaft!

  34. 7 5 6 8

  35. Base line for Sensor Values(Except as mentioned) • Normal operating temperature (cooling fans cycled twice) • Idle (closed throttle) • All accessories off • In Park or Neutral • Closed loop

  36. Skewed Sensors • A skewed sensor gives variable readings that appears to be accurate • However the sensor may be contaminated or dirty and sending incorrect information to the PCM • Does the PCM know the sensor is skewed?

  37. Data Stream Step #1 • Before starting the engine, connect the scan tool. • This step is very important, especially if the driveability concern is hard starting or cold driveability.

  38. Data Stream Step #1 (continued) • Key on/Engine off (KOEO) and look at the values for ECT (engine coolant temperature) and IAT (intake air temperature). • Basically, the same sensor and the two temperatures should agree.

  39. ECT = IAT • The two temperatures should be the same (within 5 degrees). • Both should measure the ambient air temperature. • If the two indicate different temperatures, the one closer to the ambient air temperature is the one most likely to be correct.

  40. ECT = IAT (continued) • The ECT sensor has a higher authority than the IAT and is therefore more likely to be the cause of a starting or cold running problem. • The ECT is the only sensor used by the PCM when the ignition key is first turned from on to start.

  41. Quick and Easy Metric Temperature Conversion • Double the Celsius degree number • Add 25 • Should be close to the Fahrenheit temperature • Example: 50 degrees X 2= 100+25=125 • Actual= 122

  42. Data Stream Step #2MAP= BARO • Another sensor to check is the MAP sensor because it is a high-authority sensor, especially on speed density controlled engines. • The MAP reading at KOEO should be atmospheric pressure (about 29.50 in. Hg.), depending on altitude and weather conditions. • An easier value to remember is that it should be about 4.6-4.8 volts

  43. MAP Sensor Authority • The MAP sensor is a high-authority sensor on an engine that uses the Speed-Density method of fuel control. • If the exhaust is rich, try disconnecting the MAP sensor. • If the engine now runs OK, then the MAP sensor is skewed or giving the PCM wrong information.

  44. MAP Too High or Too Low • The sensor could be skewed. • Check the power and ground of the sensor. • If 5-volt reference (Vref) is low, check other sensors that also use the reference voltage.

  45. Data Stream Step #3IAC Counts • After the engine starts, observe the IAC counts or percentage. • The IAC is used to control idle speed by changing the amount of air bypassing the throttle plate (just like depressing or releasing the throttle pedal).

  46. IAC (continued) • On a warm engine (cooling fans cycled twice), the IAC counts should be 15-25 counts or percentage. • If the IAC commanded position is low, a vacuum leak (speed density engines mostly) could be indicated. • The extra air decreases the vacuum and the MAP sensor reads this drop as an increase in load. The PCM adds fuel, increasing the engine speed.

  47. IAC Too High • If the IAC position is higher than normal. This could indicate a dirty throttle plate(s) or a vacuum leak on a MAF engine.

  48. Higher IAC • A vacuum leak on a MAF engine is actually false air not measured by the MAF sensor. This can cause the engine speed to decrease due to the leaner-than-normal air-fuel mixture. The mixture causes the PCM to increase engine speed and commands a higher IAC position. • Note: Some minor vacuum leaks can cause the IAC to drop just like on a speed density engine.