P1351 – Ignition Control Module Circuit Voltage

By Reinier (Contact Me)
Last Updated 2022-04-16
Automobile Repair Shop Owner

Manufacturer Specific Definitions for P1351

Table of Contents

1. What Does Code P1351 Mean?
2. What are the common causes of code P1351?
3. What are the symptoms of code P1351?
4. How do you troubleshoot code P1351?
5. Codes Related to P1351
6. Get Help with P1351

What Does Code P1351 Mean?

SPECIAL NOTES: Since code P1351 is primarily concerned with an abnormal voltage in the Ignition Control Module’s control (or input) circuit, we will for the purposes of this guide ignore all the other sensors that contribute to the ignition timing strategy, as well as the nature of the timing pulse, which is based on a complex relationship between primary, secondary, synching, and feedback pulses.  

Moreover, although this code has much the same meaning across nearly all major car manufacturers, there are significant design differences between the ignition systems used by different manufacturers. For this reason, non-professional mechanics are strongly urged to read the section in the manual that deals with the ignition system of the application being worked on to gain at least a working knowledge of the ignition system on that application before attempting a diagnosis of this code.

However, while this guide cannot provide detailed diagnostic and repair information that will apply to all applications under all conditions for the reasons stated above, the generic steps outlined in the Troubleshooting section of this guide should enable most non-professional mechanics to diagnose and repair this code on almost any application. END OF SPECIAL NOTES.

OBD II fault code P1351 is a manufacturer specific code that most carmakers define as “Ignition Control Module Circuit Voltage”, or sometimes as “Ignition Control Module Circuit High Voltage”. This code is set when the PCM (Powertrain Control Module) detects an abnormal voltage in the control circuit of the ICM (Ignition Control Module). Note that in the definition “Ignition Control Module Circuit Voltage”, the abnormal voltage could be either a high or a low voltage.

On engines that employ DIS (Direct Ignition, also known as Distributor-less Ignition) systems, the PCM uses input data from the Crank Position Sensor (and depending on the application, the Camshaft Position Sensor(s)) to calculate an appropriate ignition timing strategy to suit the engine speed and load at any given time. When the ignition pulse is received by the PCM, it is converted into a digital signal before being sent to the Ignition Control Module for delivery to the primary winding of the appropriate ignition coil, where the initial pulse is converted into an extremely high energy pulse in the secondary winding to initiate the combustion process through the sparkplug when the signal is interrupted by the Ignition Control Module.

In a fully functional ignition system, both the Crankshaft -, and Camshaft Position Sensors generate signal voltages of about 5 Volts, but note that this voltage can vary between applications. However, while some types of sensors generate a signal voltage through the Hall Effect; other types of sensors require an input or reference voltage to generate a signal voltage- therefore, the types of problems, failures, or malfunctions that ultimately affect the signal voltage that reaches the Ignition Control Module via the PCM are different.

For instance, an excessive air gap between a Hall-effect sensor and the reluctor ring on the crankshaft might produce an abnormally low signal voltage, while a defective alternator that overcharges might induce an abnormally high signal voltage in other types of sensor, and by extension, in the voltage that ultimately reaches the Ignition Control Module. Nonetheless, regardless of the cause of the problem, the PCM will set code P1351 and illuminate a warning light when it detects an abnormal voltage in the control circuit of the Ignition Control Module.

The image below shows a much-simplified schematic of a typical DIS ignition system. Note the relationship between the magnetic triggering device (Crankshaft Position Sensor) and the Ignition Control Module- code P1351 is primarily concerned with the voltages in the circuit between these two components, as well as with the voltages between the triggering device and the battery (not shown here) in cases where the triggering device requires an input current.

What are the common causes of code P1351?

The most common cause(s) of code P1351 – “Ignition Control Module Circuit Voltage”, are much the same across all applications that use this definition. However, some applications may have specific causes that do not occur on other applications, so always consult the manual for the application being worked on for detailed information on the causes that are most likely to produce code P1351 on that particular application. Below are some common causes of P1351-

• Damaged, burnt, shorted, disconnected, or corroded wiring and connectors
• Open circuits
• Defective/damaged Crankshaft Position Sensors
• Defective/damaged Camshaft Position Sensors (Where applicable)
• Abnormal system voltages caused by defects, malfunctions, or failures in the charging system
• Failed, or failing PCM. Note that replacing the PCM requires programming of the replacement

What are the symptoms of code P1351?

Apart from a stored trouble code and possibly an illuminated warning light, the typical symptoms of P1351 are largely make and model specific and much depends on the exact nature of the problem. Some applications might exhibit severe driveability issues, while on others the only immediately apparent symptom may be a no-start condition. However, some typical symptoms could include the following, but note that not all the symptoms listed here will always be present on all applications-

• No-start conditions may be present at all engine temperatures
• Engine may not start while it is hot
• In rare cases, the engine may start but shut off again after a few seconds
• Engine may not idle after reaching operating temperature.
• In some cases, the engine may develop serious misfires after reaching operating temperature
• If intermittent failures are present, the engine may shut off unexpectedly, or it may, or may not start in an unpredictable pattern

NOTE: This list of possible symptoms is neither complete, nor exhaustive. Always refer to the manual for the application being worked on for detailed information on the symptoms that are most likely to beset the vehicle when code P1351 is present.

How do you troubleshoot code P1351?

SPECIAL NOTES: In many cases, code P1351 is the direct result of using substandard aftermarket sensors, so one way to save a lot of diagnostic time is to check if the sensors on the application are OEM equipment as a first step in the diagnostic procedure. Many instances of this code can be resolved by replacing aftermarket sensors with OEM parts, but be aware that this does not always resolve the problem, and it might be necessary to work  through the steps outlined here to diagnose and repair code P1351. END OF SPECIAL NOTES.

Step 1

Record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.

NOTE: If any other codes are present along with P1351, these codes MUST be resolved in the order in which they were stored before attempting a diagnosis and repair of P1351, especially if any system voltage related codes are present.

Step 2

Assuming that no other codes are present, consult the manual to locate all relevant components, as well as the routing, color-coding, function, and location of all associated wiring to be sure that the correct circuits and components will be tested.

Perform a thorough visual inspection of all associated wiring and connectors, and look for damaged, burnt, shorted, disconnected, and corroded wiring and connectors. Make repairs as required, clear all codes, and rescan the system to see if the code returns.

Step 3

If no visible damage to wiring and connectors if found but the code persists, consult the manual to determine which type of crankshaft (and/or camshaft) sensors are fitted to the vehicle. If the sensors require an input voltage, consult the manual on the correct procedure to test the input voltage, and compare the obtained reading with the value stated in the manual.

If a deviation (a low voltage) is found, inspect all wiring between the sensor connector, the ignition switch, and the battery for poor connections, poor ground, or other issues that could affect continuity. Be aware though that this step involves checking and testing several individual circuits, so be sure to follow the instructions in the manual exactly to avoid causing short circuits that could damage other components and/or controllers. Note that on some applications, the PCM supplies the ground, so consult the manual on the correct procedure (KOER/KOEO) to establish the ground connection.

Compare all obtained readings with the values stated in the manual, and make repairs as required to ensure that all electrical values fall within specified values. Clear all codes after repairs are complete, and rescan the system to see if the code returns.

NOTE: Be sure to disconnect both the Ignition Control Module and the PCM from the wiring harness during resistance and /or continuity checks to avoid damage to either, or both controllers.

Step 4

Assuming that the charging system checks out OK and that the battery is not damaged or over charged on older applications, high input, or reference voltages in the Crankshaft Position Sensor circuit is almost always caused by a short circuit to the battery positive. However, this condition will almost certainly be indicated by a code other than P1351, so check again for the presence of other codes, and resolve these codes before proceeding to the next step.

Step 5

If a short circuit to battery positive is suspected, inspect all associated wiring/connectors, and repair, or replace wiring/connectors as required. Clear all codes after repairs are complete, and rescan the system to see if the code, or any other codes, returns.

NOTE: Since the Crankshaft -, and/or Camshaft Position sensors form part of the circuit, these sensors must be tested as well. Consult the manual on the correct procedure to test the sensors, and replace all sensors that do not conform to the manufacturer’s specifications.

Step 6

If the sensors do not require an input voltage, carefully check the air gap between the sensor and the reluctor wheel on the crankshaft pulley. In some cases, it is possible for the sensor retaining bolts to work themselves loose, which can cause the air gap to increase to the point where the sensor does not work.

Reset the air gap to the specified clearance, clear all codes, and rescan the system to see if the code returns. If the code persists, remove the sensor from the engine and inspect it for signs of impact damage, or evidence that it might have rubbed against the reluctor wheel. Replace the sensor if signs of mechanical damage are found, and rescan the system after the replacement to see if the code returns.

If the sensor is not damaged in any way but the code persists, consult the manual on the correct procedure to test the sensor, and replace it if it does not conform to the manufacturer’s specifications.

Step 7

If the code persists despite several repair attempts, it is likely that an intermittent fault is present, which can sometimes be found by “wiggling” all connectors and wiring while the voltage in a circuit is being monitored with a multimeter. If there is an intermittent fault present, the reading     displayed on the multimeter will often change in direct response to the “wiggle” test, but be aware that some intermittent breaks, short circuits, or losses of ground connectivity in wiring do not always respond to this test.

Therefore, the better option if an intermittent fault is suspected is to refer the vehicle for professional diagnosis and repair, since the diagnosis and repair need to be definitive and reliable.

Step 8

The generic diagnostic/repair steps up to this point will usually resolve nine out of every ten instances of code P1351, but in some cases, the code involves abnormal voltages between the PCM and the Ignition Control Module.

The diagnostic steps required to diagnose this condition are make and model specific, but unless a wiring problem between the PCM and the Ignition Control Module is identified, the only remedy for this condition involves replacement of the PCM. Take note that replacing a PCM requires programming of the replacement PCM, which is a procedure best left to professional technicians who have access to the required equipment and software.

Also, note that testing for PCM faults require testing pins and terminals on the PCM itself, which requires a pin-out chart for that specific application and PCM. DO NOT attempt to test ANY circuit on a PCM if a pin-out chart and repair manual is not available. Doing so could not only destroy the PCM, but several other controllers as well. If a defective PCM is suspected, the better option is to refer the vehicle for professional diagnosis and repair.

Codes Related to P1351

Related codes are make and model specific, which means that the manual for the application must be consulted for detailed information related codes that could conceivably cause, or contribute to the setting of P1351.

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