P1520 is a manufacturer-specific OBD-II diagnostic trouble code. Its exact definition depends on the vehicle application, commonly relating to an intake manifold runner control fault or a vehicle speed sensor circuit issue.
Because definitions vary by manufacturer, the exact diagnostic path requires verifying your specific vehicle’s factory service information. The code identifies a detected condition, not necessarily a failed part.
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Key Takeaways
- P1520 is a manufacturer-specific code indicating a fault in the intake manifold runner control (IMRC) system or the vehicle speed sensor (VSS) circuit.
- Possible causes include a broken IMRC linkage, failed actuator, damaged VSS, or wiring issues.
- Symptoms may include poor low-end acceleration, erratic speedometer readings, or transmission shifting issues.
- Diagnosis requires verifying the exact factory definition and testing the relevant IMRC or VSS circuits.
P1520 Code Description and Implications
P1520 is a manufacturer-specific code, meaning its exact definition varies by automaker. The powertrain control module uses this code to flag an anomaly within a specific engine management or speed monitoring system.
Some Ford applications: P1520 indicates a malfunction in the Intake Manifold Runner Control (IMRC) circuit. The module detects an error with the IMRC actuator, monitor switch, or linkage.
Certain GM applications: This code points to an intermittent fault in the Vehicle Speed Sensor (VSS) circuit or a Park/Neutral Position switch circuit issue.
Because the code is manufacturer-specific, you must verify the exact factory definition for your vehicle before beginning diagnosis. The specific error code meaning dictates the test.
Common Causes of the P1520 Code
IMRC system faults (Ford applications): A broken or binding IMRC cable, a failed IMRC actuator motor, or a faulty monitor switch can prevent the manifold runners from opening or closing correctly.
VSS circuit faults (GM applications): A damaged vehicle speed sensor, metal debris on the sensor tip, or chafed wiring can cause an intermittent speed signal.
Wiring and connector damage: Harnesses routing to the IMRC actuator or VSS are exposed to engine heat and vibration, which can lead to open or shorted circuits.
Symptoms Associated With P1520
Because this code affects either intake airflow or speed sensing, symptoms depend on the vehicle’s specific implementation.
On IMRC applications, you may experience poor low-end torque, sluggish acceleration, or a lack of power as the intake runners fail to adjust for engine RPM.
On VSS applications, you may notice an erratic or dead speedometer, harsh transmission shifting, or inoperative cruise control.
You will see an illuminated check engine light across most applications when this code is stored.
Diagnosing the P1520 Trouble Code
Diagnosis must begin by confirming the exact factory definition and wiring diagram for your specific make, model, and year. Retrieve freeze frame data to understand the conditions when the code set.
For Ford IMRC applications, visually inspect the IMRC linkage and cable for binding, breakage, or disconnection. Command the IMRC actuator using a scan tool to verify operation and test the monitor switch circuit.
For GM VSS applications, inspect the speed sensor and its wiring. Monitor the VSS data on a scan tool while driving to check for signal dropouts.
Repairing the P1520 Issue
Repairs must follow confirmed diagnostic testing. Do not replace the IMRC actuator or VSS without verifying the wiring harness and checking for mechanical binding first.
If the IMRC cable is broken or binding, repair or replace the linkage assembly. If the VSS is contaminated with metal debris, clean the sensor tip.
If the component fails electrical testing, replace it with a part meeting the exact vehicle specification, then clear the codes.
Cost Considerations for P1520 Repairs
Repair costs depend on the confirmed root cause, component accessibility, and local labor rates. Replacing an external VSS or repairing a simple linkage is generally straightforward.
If the IMRC actuator requires replacement or the intake manifold must be removed for internal runner repairs, parts and labor costs will increase. Always factor in the cost of proper diagnostic time.
Prevention Strategies for Future Occurrences
Inspecting exposed wiring and electrical connectors during routine maintenance can help identify developing heat damage or chafing before it causes a circuit fault.
On applications using an IMRC cable, ensuring the linkage remains lubricated and free of carbon buildup helps prevent mechanical binding.
Troubleshooting Tips and Best Practices
Always verify the exact definition of P1520 for your specific vehicle. Assuming it is always an intake manifold issue can lead to misdiagnosis when a vehicle speed sensor fault is the actual cause on a GM application.
Do not ignore related codes. If P1520 is accompanied by other IMRC or VSS codes, it strongly supports a shared wiring harness issue or a failing component assembly.
Check for technical service bulletins related to updated IMRC actuators or VSS connectors for your specific model year.
More OBD-II Codes
| P1519 | P1518 | P1516 | P1513 |
| P1512 | P1511 | P1521 | P1524 |
| P1525 | P1529 | P1542 | P1550 |
| P0500 | P0501 | P0502 | P2004 |
| P2005 | P2006 | P2008 | P2009 |
| P1478 | P1477 | P1397 | P1188 |
Frequently Asked Questions
Is P1520 a generic or manufacturer-specific code?
No. P1520 is a manufacturer-specific code. Its exact definition and diagnostic procedure vary depending on the vehicle make, model, and year. Always consult the factory service information.
Can a broken IMRC cable cause a P1520 code?
Yes. On Ford applications, a broken or binding IMRC cable prevents the intake runners from adjusting, causing the module to detect an actuator or monitor error and store this code.
Is it safe to drive with a P1520 code?
Driving is generally safe for short distances. However, an IMRC fault will reduce low-end acceleration, and a VSS fault can cause erratic transmission shifting or disable cruise control.
Will replacing the vehicle speed sensor always fix P1520?
Not always. P1520 indicates a circuit or performance fault. The root cause could be damaged wiring, metal debris on the sensor, or a module issue. Proper electrical testing is required first.
Can an intake manifold leak trigger P1520?
On most verified applications, P1520 relates specifically to the IMRC actuator circuit or the VSS circuit, not a general vacuum leak. Assuming it is a leak can lead to misdiagnosis.
What Should You Do About the P1520 Code?
Confirm the exact factory definition and wiring diagram for your specific vehicle application. Inspect the relevant intake manifold runner controls, vehicle speed sensors, and connectors for physical damage or mechanical binding.
Perform targeted electrical and mechanical testing on the relevant system and components to isolate the fault. Repair the confirmed root cause, then verify the repair by clearing the codes and monitoring live data.
