How do you fix the ignition distributor engine speed input circuit?

The quickest fix is to identify and replace the faulty distributor pickup or ignition module, repair worn or damaged wiring, and re-time the engine. This signal path is essential for proper ignition timing and engine response.

In distributor-based ignition systems, the engine speed input is the electrical signal from the distributor that tells the ignition control module (or ECU) how fast the engine is turning. When this signal is degraded or lost—due to a bad pickup coil, damaged wiring, a failing ignition module, or a poor ground—the engine can misfire, stall, or fail to start. This article outlines how to diagnose and repair the speed input circuit with current best practices, tools, and safety considerations.

Understanding the speed input circuit

The speed input circuit relies on the distributor’s pickup to generate a pulsed signal that the ignition control system uses to time sparks. In older vehicles, this signal is often processed by a separate ignition module integrated in the distributor or by the ECU. Modern scenes may vary, but the basic principle remains: a clean, reliable signal is required for consistent timing and reliable starting.

Common failure modes

The following issues are frequently responsible for a degraded speed input signal. Diagnosing them early can prevent unnecessary part replacement and keep the engine running smoothly.

• Worn or failed distributor pickup coil (including Hall-effect or reluctor-based sensors).


• Damaged, pinched, or corroded wiring and connectors between the distributor and the ignition module/ECU.


• Faulty ignition control module inside the distributor or in the wiring harness.



• Worn or misaligned reluctor ring or rotor, causing faulty signal timing.


• ECU or wiring software glitches affecting signal interpretation.

These issues can produce intermittent or no spark, erratic tachometer readings, or a no-start condition, especially under load or at certain RPM ranges.

How the signal should behave

A healthy speed input typically presents as a clean, repeatable waveform or digital pulses when monitored with the right diagnostic tools. Any irregularities, missing pulses, or inconsistent amplitude usually point to a faulty sensor, damaged wiring, or a compromised ground.

Diagnostics and testing

To diagnose the speed input circuit, technicians use a structured approach that combines visual inspection, electrical tests, and waveform analysis.

These steps outline a common diagnostic sequence for distributor-based ignition systems.

1. Inspect the entire wiring harness and connectors for damage, heat damage, corrosion, or loose connections. Pay particular attention to grounds and power feeds to the distributor and ignition module.


2. Verify the battery voltage and ignition switch supply to the distributor/module; ensure a solid 12V (or specified voltage) with the key on.


3. Check grounding: ensure a solid engine ground and, if applicable, a dedicated ground strap between the module and engine block.


4. Measure the distributor pickup coil resistance and continuity according to the vehicle’s service manual. Replace the pickup if the resistance is out of spec or if there is an open/short path.


5. Observe the signal with an oscilloscope or a high-quality scan tool that can display the ignition trigger waveform. Look for clean, regular pulses with consistent amplitude; any dropped pulses or irregular timing indicates a faulty sensor or wiring.


6. Test the ignition control module (or the ECU input) using a known-good module or by swapping a compatible unit to verify whether the fault lies in the module or upstream.


7. Inspect the reluctor ring and distributor mechanical alignment. Check for excessive play, bent teeth, or rotor wear that could disrupt the signal.

Following these steps helps isolate whether the fault is the pickup sensor, the wiring, the grounding, the module, or a mechanical issue within the distributor.

After completing this diagnostic sequence, you should have a clear sense of which component is failing and whether replacement is warranted.

Repair and replacement options

Once a fault source is identified, choose the repair path that restores reliable speed input while balancing cost and reliability. The options below reflect common industry practice.

• Replace the distributor pickup coil or the entire distributor assembly if the sensor itself is worn or damaged beyond repair.


• Replace the ignition control module (internal to the distributor or in the wiring harness) if it shows signs of failure or intermittent operation.


• Repair or replace damaged wiring, connectors, or grounding straps; use proper insulation, crimping, and sealing to prevent future corrosion.


• In some cases, replace the ECU/PCM if it is failing to interpret a healthy signal correctly or if it has developed a fault that affects the input channel.


• Perform a timing recheck and realignment after replacement to ensure optimal ignition timing and engine performance.

After completing repairs, test the system again with a waveform/scan tool to confirm a clean speed input, then conduct a road test to confirm the engine runs smoothly under varying loads and RPM.

Safety and best practices

Working on ignition systems involves high voltage and moving parts. Always disconnect the battery before service, follow manufacturer torque specs, and wear eye protection. If you’re unsure about the correct procedure or timing specification for your vehicle, consult the service manual or a qualified mechanic.

Summary

Fixing the ignition distributor engine speed input circuit comes down to verifying the integrity of the distributor pickup, its wiring, and the ignition control module, then replacing the faulty components and re-timing the system. Use a methodical diagnostic approach: inspect wiring, test continuity and resistance, observe the trigger signal with appropriate tools, and replace failing parts as needed. When in doubt, seek professional help to ensure safe, accurate repairs and reliable engine performance.

What is the ignition distributor engine speed input circuit malfunction?

DTC P0320 stands for “Ignition/Distributor Engine Speed Input Circuit.” It's logged when the PCM detects that the CKP sensor doesn't transmit signals after the CMP sensor. A defective CKP sensor, a bad CMP sensor, a damaged crankshaft (or camshaft sensor tone wheel), and a malfunctioning PCM can trigger the error code.

What is the engine speed input circuit malfunction?

Chances are very high that the error code is a result of a faulty sensor or circuit. If the sensor itself is damaged, then it makes sense that it would send this error code. There may also be metal deposits on the sensor. However, the problem may be electrical in nature, rather than mechanical.

How serious is the P0320 code?

Because OBD-II scanner error code P0320 problem is considered a fault in the electrical circuit, there may not be many performance issues. You'll simply see the malfunction indicator light and your OBD-II scanner will read code P0320. However, a fault in either the CKP or CMP could prevent your engine from starting.

How to fix code P0320?

To fix P0320, start by inspecting and replacing a faulty crankshaft or camshaft position sensor, as these are the most common culprits. Next, check the sensor wiring for damage like shorts or corrosion, and ensure the power and ground connections are sound. In some cases, an ignition coil failure can also cause this code, and its wiring should be inspected as well. 
Step 1: Inspect and test sensors and wiring 

• Crankshaft/Camshaft position sensors: These are the most common causes. Visually inspect them for damage and test them with a multimeter for proper resistance and voltage, consulting your vehicle's service manual for the correct specifications.
• Wiring and connectors: Look for any signs of damage, such as broken wires, shorts, or corrosion, especially at the sensor connectors. Check the voltage supply, ground, and signal wires for the circuits. 

This video demonstrates how to inspect wiring for damage and clean connectors: 1mCar A-ZYouTube · Jan 13, 2024
Step 2: Replace faulty components 

• If the sensors or wiring are faulty, replace the defective part. Start with the crankshaft position sensor, as it is more frequently the issue. 
• If the problem persists after replacing the sensor, move on to the camshaft position sensor. 
• Repair or replace any damaged wiring harnesses or connectors. 

Step 3: Check other potential issues

• Ignition coils: A failing ignition coil can cause a P0320 code, often accompanied by engine misfires or other related codes. Inspect the coils and their connectors, as a loose connection is a common problem. 
• Battery voltage: Low battery voltage can sometimes cause this code. Check your battery's health and repair any low voltage conditions. 
• Distributor: In older vehicles, the issue could be with the distributor itself. 

Step 4: Clear the code and verify the fix 

• After making repairs, clear the code using an OBD-II scan tool. 
• Start the engine and check if the code returns. If it does, further diagnosis is necessary. 
• Consider driving the vehicle to see if the code reappears, as some issues are intermittent.