ASE A8 computerized engine controls practice questions.

Five free practice questions on computerized engine controls: content area E of the ASE A8 Engine Performance test, 13 of its 50 scored questions (26%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.

01The questions

1. Tech ab · Computerized Engine Controls Diagnosis and Repair

   A scan tool's readiness screen lists a vehicle's secondary air monitor as 'not supported' and its catalyst monitor as 'incomplete'. Technician A says 'not supported' means the vehicle was not built with that monitor. Technician B says 'incomplete' means the catalyst monitor ran and found a fault. Who is right?

   1. A only
   2. B only
   3. Both A and B
   4. Neither A nor B
   Show the answer

   A. Correct. Technician A is right: 'not supported' is the PCM reporting that the vehicle has no such monitor, as on an engine built without secondary air. Technician B is wrong: 'incomplete' means the monitor has not yet run to completion since memory was last cleared; a failed monitor sets a DTC instead.

   Why not the others

   B. Not B only. Technician B is wrong: 'incomplete' means the monitor still needs more driving to finish its test, not that it failed. Technician A is right that 'not supported' means the vehicle has no such monitor.

   C. Not both. Technician A is right about 'not supported', but Technician B is wrong: 'incomplete' means the catalyst monitor has not yet finished its test; a fault would set a DTC.

   D. Technician A is right, so not neither: 'not supported' means the vehicle was built without that monitor. Technician B is wrong because 'incomplete' means the test has not finished, not that it failed.

2. Diagnosis · Computerized Engine Controls Diagnosis and Repair

   A vehicle's MIL went out months ago after a repair, but the scan tool still shows the DTC stored. The owner makes only short winter trips, and recorded data show the coolant rising from about 20°F to a peak of about 125°F on each trip. Which of these explains why the DTC is still stored?

   1. The MIL must be on for a DTC to be erased
   2. A stored DTC can be erased only by a scan tool
   3. The DTC became permanent when the MIL went out
   4. None of the trips counted as a warm-up cycle
   Show the answer

   D. Correct. OBD II lets the PCM erase a DTC once the fault has not returned for 40 warm-up cycles, and a warm-up cycle needs the coolant to rise at least 40°F from start and reach at least 160°F. Trips that peak near 125°F never count, so the code stays stored.

   Why not the others

   A. This is reversed: the self-erase rule applies to a code whose MIL is off. The code remains because the coolant never reaches the temperature a warm-up cycle requires.

   B. The PCM may erase a DTC on its own after enough warm-up cycles without the fault. The code remains here because none of these trips qualified as a warm-up cycle.

   C. A permanent DTC is erased when the monitor proves the fault gone, which is what lets the MIL go out; it does not begin then. The stored code remains because no trip has counted as a warm-up cycle.

3. EXCEPT · Computerized Engine Controls Diagnosis and Repair

   A warm engine runs smoothly and has no DTCs, but a five-gas analyzer shows high NOx at the tailpipe while the vehicle is under load on a chassis dynamometer. Any of these could cause the high NOx EXCEPT:

   1. an upstream oxygen sensor biased rich.
   2. a catalytic converter that has lost efficiency.
   3. an engine running hotter than normal.
   4. a rich mixture from high fuel pressure.
   Show the answer

   D. Correct. NOx forms when nitrogen and oxygen combine at high combustion temperature, and a rich mixture leaves little free oxygen and burns cooler, so it lowers NOx while raising CO and HC. High NOx points to hot combustion, too little converter action or a lean condition instead.

   Why not the others

   A. A sensor that reads richer than the real exhaust makes the PCM take fuel out, so the engine runs lean, and the extra oxygen in a lean mixture lets more NOx form. This could cause it.

   B. A three-way converter is what reduces NOx back to nitrogen in the exhaust; one that has lost its efficiency lets the engine's NOx pass to the tailpipe. This could cause it.

   C. A hotter engine means hotter cylinder walls and intake charge, which raise peak combustion temperature, and NOx formation rises with it. This could cause it.

4. EXCEPT · Computerized Engine Controls Diagnosis and Repair

   Each of these is an acceptable way to take a voltage reading on a PCM sensor circuit EXCEPT:

   1. connecting a breakout box between harness and PCM.
   2. using the terminal test adapter the manufacturer lists.
   3. forcing a meter probe into a female terminal.
   4. backprobing an unsealed connector beside the wire.
   Show the answer

   C. Correct. A standard meter probe is larger than the mating pin, so forcing it into a female terminal spreads the terminal. The spread terminal then grips loosely and can cause the very intermittent fault being chased.

   Why not the others

   A. A breakout box gives a test point for every PCM terminal without disturbing the terminals or seals. This is acceptable.

   B. The manufacturer's adapter is sized to the terminal, so it makes contact without spreading it. This is acceptable.

   D. A thin backprobe slid in beside the wire at the rear of an unsealed connector touches the terminal without harming it. This is acceptable.

5. EXCEPT · Computerized Engine Controls Diagnosis and Repair

   When the transmission or traction control module asks the PCM to reduce engine torque, the PCM can do it by any of these EXCEPT:

   1. retarding the spark timing.
   2. closing the electronic throttle part of the way.
   3. shutting off fuel to some cylinders.
   4. opening the electronic throttle further.
   Show the answer

   D. Correct. Opening the throttle admits more air and raises torque, the opposite of what the request asks for. Torque is reduced by retarding spark, closing the throttle or cutting fuel to some cylinders.

   Why not the others

   A. Retarding spark moves combustion later and lowers torque quickly. This is a method the PCM uses.

   B. Closing the throttle reduces airflow and so torque. This is a method the PCM uses, though it acts more slowly than spark retard.

   C. Cutting fuel to selected cylinders removes their power strokes and is used for large, fast torque cuts. This is a method the PCM uses.

02Answer key

03What area E covers

This content area covers the PCM and the OBD II system that watches the engine: reading DTCs, freeze frame and monitor status, how codes set, go pending, light the MIL and clear, testing sensors, actuators and circuits with a scan tool, DMM and lab scope, PCM power and ground circuits, programming, faults from related systems, data network problems and verifying a repair.

The ASE test specification calls this content area “Computerized Engine Controls Diagnosis and Repair”. It carries 13 of the 50 scored questions, 26% of the test.

• Retrieve DTCs, freeze frame and readiness status
• Research enable criteria and how DTCs set and clear
• Diagnose driveability faults with and without DTCs
• Test sensors, actuators and circuits with meters and scopes
• Check PCM power feeds and ground circuits
• Replace, program and set up the PCM
• Diagnose related systems and data network faults
• Clear DTCs, run monitors and verify the repair

04What the questions turn on

Pending, confirmed and permanent

On a two-trip fault, the first detection is stored as a pending DTC with the MIL off and becomes confirmed if seen on the next trip. A scan tool cannot clear a permanent DTC. The PCM erases it once its monitor runs and passes.

Record before you clear

Clearing DTCs also erases freeze frame data and resets readiness monitors, so the codes and freeze frame are recorded first. A drive that repeats the freeze frame conditions without a new pending DTC is good confirmation of the repair.

Monitors need their conditions

Each monitor runs only when its enable criteria are met, such as a set speed range, steady cruise or a cold soak. Driving outside that window, or only idling, leaves the monitor incomplete however long the drive lasts.

References and sensor grounds

Many sensors ground through the PCM so the sensor and the PCM read from the same ground reference. A voltage drop along a 5-volt reference wire leaves the sensor less than 5 volts, and its signal reads low.

05The other content areas

The A8 test has five content areas. Each has its own page of free questions:

The ASE A8 Engine Performance practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.

ToolboxPrep is an independent study site. It is not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original practice questions written to the published ASE test specifications; they are not actual test questions.