1. A Step-by-Step Guide to Success
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
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.
The flow chart for PO304 led us to a dead end. A TSB search came up with
bulletin# and the information above was found under the “diagnostic information” section for that TSB
The highlighted info from above is :
If all procedures have been completed , and the misfire concern is still present use the following steps.
a. Remove the upper intake manifold and check the Egr orifices that are pressed into the primary intake port of the lower intake manifold. If any Egr orifice is missing , replace lower intake manifold with a new lower intake manifold. If any or the orifices are plugged with soot, clean and un-plug them with a pick and solvent. Refer to factory manual for servicing the upper and lower manifolds.

26. Remove upper plenum for EGR inspection.
Removal of the upper plenum isn’t that bad a job. Flat rated at 1.3 hours . Gasket set list is approx $ $30.00

27. Note that 5 out of the six are plugged up 100%
Note that 5 out of the six are plugged up 100%. Ford suggests that if any of these are loose in manifold to replace lower unit with a new unit operation # cb ( additional 3.2 hours )
The thought here is that the egr flow cant get to the five cylinders and diverts all ( based on stoppage) to the cylinder # 4 causing the misfire on cylinder four when under load.
5 out of 6 are stopped up!

28. Pick/remove deposits from egr passages and smoke test to verify
Pick/remove deposits from egr passages and smoke test to verify. The clog seem to be only at the discharge end. There does NOT seem to be a complete clog of the passage from the EGR to the discharge port. This makes them very easy to clean!

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

30. 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

31. Rough Idle; Surge; No Codes

32. Gear Wear!

33. Gear /Pin / Washer Kit Available

34. Plate spins on shaft!

35. 7 5 6 8

36. 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

37. 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?

38. 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.

39. 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.

40. 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.

41. 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.

42. 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= =125
Actual= 122

44. Data Stream Step #2 MAP= 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 in. Hg.), depending on altitude and weather conditions.
An easier value to remember is that it should be about
volts

45. 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.

46. 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.

47. Data Stream Step #3 IAC 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).

48. IAC (continued)
On a warm engine (cooling fans cycled twice), the IAC counts should be 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.

49. 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.

50. 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.

51. Data Stream Step #4 MAF Sensor
Look at the amount of air entering the engine.
There should be:
3 to 7 grams per second (g/s)
About 1 volt (analog MAF sensor)
About 0.5 lb. per hour
About kilograms per hour (kg./hr)

52. Normal MAF Readings Use a scan tool to look at the grams per second.
Warm the engine at idle speed with all accessories off. Should read 3 to 7 grams per second.
GM 3800 V-6 should read 2.37 to 2.52 KHz.
If not within this range, check for false air or contamination of the sensor wire.

53. MAF Sensor Diagnosis
If the MAF sensor wire were to become coated, it cannot measure all of the incoming air.
A normal warm engine at idle should be 3 to 7 grams per second.
Rapidly depress the accelerator pedal to WOT. It should read over:
100 grams per second (scan tool) or
higher than 7 kHz (digital MAF sensor)
4 volts (analog MAF sensor)

54. Visual Inspection Look for a very dirty filter.
Look for a K & N filter that has been over-oiled.
Look for fuzz on the sensing wire from fibers coming off of the filter paper.

55. Fuzzy MAF

56. Mass Air Flow (MAF)-False Air
Usually affects operation in drive; may run OK if driving in reverse.

57. MAF Sensor Authority High-authority sensor If in doubt - Take it Out!
If the MAF sensor is disconnected, the PCM substitutes a backup value.
If the engine runs OK with the MAF disconnected, then the MAF has been supplying incorrect information.

58. Data Stream Step #5 Injector Pulse-Width
On a warm engine, the injector pulse-width should be
1.5 to 3.5 milliseconds.

59. Injector Pulse-Width Too Long
If the PW is higher than normal (higher than 3.5 ms):
Extra load on the engine, such as the AC is on or other accessory.
Engine has a vacuum leak or some other fault, causing a leaner-than-normal air-fuel mixture.

60. Injector Pulse-Width Too Short
If the injector pulse width is shorter than 1.5 ms, the
engine could be getting fuel from some other source such as:
from the EVAP system
(purge valve stuck open)
from the fuel in the crankcase being drawn in through the PCV system
from a bad fuel pressure regulator

61. Data Stream Step #6 Oxygen Sensor
Look at the oxygen sensors for proper operation.
Upstream sensors should fluctuate higher than 800 mv and lower than 200 mv.

62. Oxygen Sensor Authority
The O2S is a high-authority sensor when the engine is operating in closed loop.
The sensor can add or subtract up to 25% from the base pulse width (some vehicles even more).
If the sensor is skewed, it can create a driveability problem.
If in doubt, take it out.
If the sensor voltage is not connected, the PCM will go into open loop.

63. Downstream Oxygen Sensor
The downstream oxygen sensors should be relatively stable and not show too much change in the voltage.

64. Data Stream Step #7 Fuel Trim
Short-term fuel trim (STFT) is used by the PCM to correct for exhaust readings that are slightly rich or slightly lean.
STFT can add or subtract fuel quickly.
STFT can add or subtract only a limited amount of fuel.

65. Long Term Fuel Trim
Long-term fuel trim (LTFT) can add or subtract more fuel than STFT.
LTFT is slower than STFT.
The purpose of LTFT is to keep STFT within plus or minus 10%.

66. LTFT and STFT Diagnosis
I suggest that you ignore STFT.
STFT is what is happening this instant.
LTFT gives a history of the exhaust mixture and is more helpful when it comes to a diagnosis.
Add the two together to get total amount of added or subtracted fuel.
LTFT = +8%, STFT = -3%, total = +5%.

67. LTFT Numbers
Ignore any fuel trim numbers less than 10%.

68. +LTFT Too High Look for a vacuum leak.
Look for a cracked exhaust manifold.

69. -LTFT Too High Check for too high fuel pressure.
Check for a leaking fuel pressure regulator.

70. Fuel Trim Example
LTFT = +12%
STFT= +2%
How is the engine running now?

71. Fuel Trim Example Answer:
The engine is operating OK now because the PCM has compensated for a slightly lean air-fuel mixture by increasing the injector pulse-width by about 14%.
Look for a vacuum leak or low fuel pressure.

72. Fuel Trim Cells
Computers use 16 or more cells for fuel trim corrections.
Look at the fuel trim numbers in the cell where the problem is occurring.
For example, looking at the fuel trim numbers at idle, will not show what is happening under a load at highway speed.

73. Plotting Snap Shot Data
The trick is to look at the range of sensor values along the side.
The range represents the high and the low values recorded for that sensor.

74. Pin Down to a System or Cylinder
Compression Test
Cylinder Leakage Test
Running (Dynamic) or Relative Compression Test

75. Pontiac Grand Prix Case Study (1997 3100 V-6)
Misfiring at idle on cylinders one, three, and five only
No DTCs
When first started, I noticed slow, jerky cranking even with the ignition disconnected (this was not a customer concern).
What would you do first?

76. Visual inspection discovered a corroded cable

77. Injector inspection showed that the wiring for the front and rear banks were switched.

78. ATF was used through the intake to check to see if the valves were sticking.

79. Spark testers were installed to check the ignition system for proper operation

80. Based on information from the archives of www. iatn
Based on information from the archives of www. iatn.net, the intake gasket area was checked for possible leaks

81. Spraying around the injector O-rings caused a misfire

82. Checking the misfire counters confirmed that we had discovered the root cause

83. Final Result
Replacing the injector O-rings solved the misfire on cylinders 1, 3, and 5.
Switching the injector harness back to the correct bank of the injectors solved the slow, jerky cranking

84. What I Learned
I learned to use the misfire counter whenever working on a possible engine misfire
The misfire counters picked up misfires that could not be detected otherwise.

85. Fuel Delivery System Check Test Drive Analysis
Low power complaint
Drive will consist of WOT.
Please check the oil level first!
Watch MAP and O2 sensor reaction.

86. Must maintain at least 850mV

87. Test Drive Analysis
If MAP does not go high ( volts); there is an intake restriction.
Look for clogged air passages.
If O2S voltage goes low; the fuel system is likely going lean.
Look for a weak pump or a clogged fuel filter.

88. Fuel Pump Pressure Test
All fuel pumps should produce a maximum pressure (deadhead pressure) about two times the operating pressure.
Normal operating pressure is 35 psi to 45 psi.(returnless systems are higher)
Maximum pump pressure should then be between 70 psi and 90 psi.

89. Quick and Easy Test
Remove fuel pump relay and install a fused jumper lead between terminals #30 and #87.
Use a stethoscope and listen for fuel returning to the fuel tank.
If fuel is not heard, then either the pump is weak or the regulator is defective.

90. Checking Fuel Pressure
Connect the gauge to the Schrader valve.
Record the pressure with engine at idle speed.

91. Checking Fuel Pressure (continued)
Rapidly accelerate the engine and watch the pressure gauge.
If the pressure drops more than 2 PSI, the fuel filter is partially clogged or the pump is weak.

92. Vortec Fuel Delivery
60PSI
55PSI

93. Case Study Chrysler mini van no-start
Customer stated that it would not start unless he pounded on the dash. Finally, the vehicle wouldn’t start at all.
Step #1-Verify
Engine did not start
No spark
No Squirt

94. Step#2- Visual Inspection
Yep the customer pounded on the dash
So hard that the needles fell off

95. Step #3 Check DTCs

96. Step #4 Checked for TSBs-nothing that was related
Checked archives of
Bingo- found several fixes for wiring being burned near the CPK sensor

97. Step #5 Scan Data
No engine RPM while cranking

98. Step #6- Narrow Down

99. Step # 6-Continued

100. Step #7 Root Cause

101. Step #8-Verify Repair

102. Summary Check monitor status and DTCs early in the diagnostic process
Always follow the same routine while diagnosing problems
Use all resources possible including:
iatn.net
Identifix (free to NATEF certified programs)
Factory and/or aftermarket service information

103. Contact Information