For young and older technicians alike, it is often tempting to jump right into component testing. This approach relies too greatly on vehicle pattern failures and luck. Improper approaches to system diagnosis are especially ineffective for intermittent faults. These type of vehicle faults are often triggered under specific conditions which are seldom present during test-bay evaluations. The example below highlights the difference between intermittent and symptom based faults and codes.

 Example: A failing fuel-pump motor will not affect engine running quality or fuel-trim at idle in a service bay but will induce drivability faults under higher load conditions. A current test evaluation of the pump circuit, at idle in the service bay, will uncover bad segments in the electric motor.

For effective and efficient trouble code diagnosis, a robust Scan Tool is critical. A professional mechanic and diagnostician will leverage their abilities with a multitude of Scan Tool features:

1. Bi-directional Controls
2. Mode $06
3. Freeze Frames
4. Memory Resets and Relearns
5. System Tests

All drivability faults are caused by one of the following engine system categories:

1. Air (engine breathing)
2. Ignition (including other cylinder contribution factors)
3. Fuel (including supply/volume and closed-loop Fuel Trim system)
4. Mechanical (only in rare cases)

Eliminating engine systems that are adequately performing will narrow down the number of potential causes for the drivability issue. With fewer systems remaining to be considered there will be less components to evaluate and tests to execute. Reducing the number of variables increases both efficiency and the likelihood of achieving a successful diagnosis. The following high-level tests are good options for isolating the engine system responsible for the fault condition:

1. Volumetric Efficiency (or calculated load at WOT)
2. Ignition, primary and secondary (cylinder contribution tests)
3. Fuel Trim (under varying conditions)

To increase the probability of duplicating a drivability symptom, every effort should be made to perform the aforementioned tests under conditions in-line with those present when the fault originally occurred . While conducting these test will eliminate categories which can be removed from consideration; hopefully, the fault will occur and be captured and identified by the technician.

Intermittent drivability faults are some of the hardest to resolve. Therefore, to effectively tackle these issues on complex vehicle systems requires a clear and repeatable strategy for performing diagnostics at the professional level. The team at Hollenshade’s in Towson includes veteran technicians who push the industry standard for accuracy and efficiency of vehicle system diagnosis and repair.

Diagnostic Trouble Codes (DTC) are set by the Comprehensive Component Monitor (CCM). Code descriptions can routinely be misleading or indicate a simple circuit malfunction for a much more complex issue. There are also many non-CCM codes. Traditionally these point to a sensed relationship or condition. Due to the complex nature of modern-era vehicle systems “shot-gunning’ parts is minimally effective. The team at Hollenshade’s in Towson employs a disciplined and repeatable process developed over 80 years of service.