P1691 is a manufacturer-specific diagnostic trouble code, meaning its exact definition depends entirely on the vehicle make.
On some applications, it indicates a fuel injection pump calibration error, while on others, it points to a coolant gauge circuit fault or an immobilizer issue.
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Key Takeaways
- P1691 is a manufacturer-specific code, and its definition varies significantly by vehicle make.
- On certain Dodge, Chrysler, and Jeep diesel applications, it indicates a fuel injection pump controller calibration error.
- On specific GM, Honda, and Acura applications, it typically signifies a coolant gauge circuit low voltage condition.
- For some Hyundai and Kia vehicles, it points to an immobilizer antenna coil error preventing the engine from starting.
- Diagnosis requires verifying the exact factory definition for your specific vehicle before testing any components.
P1691 Code Description and Implications
P1691 is a manufacturer-specific powertrain code, and its exact definition depends on the vehicle application.
Certain Dodge, Chrysler, and Jeep diesel applications: P1691 indicates a Fuel Injection Pump Controller Calibration Error.
The powertrain control module detects that the calibration values stored in the fuel injection pump controller do not match expected parameters.
Specific GM, Honda, and Acura applications: P1691 typically signifies a Coolant Gauge Circuit Low Voltage condition.
The control module detects that the signal voltage on the instrument cluster coolant temperature gauge circuit has dropped below the normal operating range.
Some Hyundai and Kia vehicles: P1691 points to an Immobilizer-Antenna Coil Error.
The immobilizer system fails to communicate properly with the key transponder due to an antenna coil fault, which may prevent the engine from starting.
Common Causes of the P1691 Code
Because the code definition varies, the causes depend entirely on the verified system.
For Dodge, Chrysler, and Jeep diesel applications, a faulty fuel injection pump or internal controller failure is one possible cause.
Wiring issues or corroded connectors between the engine control module and the injection pump can also trigger this code.
For GM, Honda, and Acura coolant gauge applications, a short to ground or open circuit in the wiring is a frequent cause.
A faulty instrument cluster or poor electrical connections at the gauge cluster harness may also set this code.
For Hyundai and Kia immobilizer applications, a failed antenna coil around the ignition cylinder is a primary suspect.
Damaged wiring connecting the antenna coil to the immobilizer control unit can also prevent proper key recognition.
Symptoms Associated With P1691
Symptoms vary widely based on the affected system and the exact vehicle application.
On diesel applications with a fuel injection pump calibration error, you may experience rough idling, reduced engine power, or poor fuel economy.
On applications with a coolant gauge circuit fault, the primary symptom is an inoperative or erratic coolant temperature gauge on the dashboard.
The engine may otherwise run normally, though the check engine light will likely illuminate.
On vehicles with an immobilizer antenna error, the most common symptom is a no-start condition.
The engine may crank normally but will not start because the immobilizer system does not recognize the key.
Diagnosing the P1691 Trouble Code
Diagnosis must begin by confirming the exact factory definition for your specific make, model, and engine.
For fuel injection pump applications, a scan tool capable of accessing diesel-specific data is required to monitor calibration parameters.
Technicians typically inspect the wiring harness between the engine control module and the injection pump before condemning the pump itself.
For coolant gauge circuit applications, diagnosis involves checking the reference voltage and signal circuits using a digital multimeter.
For immobilizer applications, diagnosis requires verifying the antenna coil resistance and checking for power at the control module connector.
Repairing the P1691 Issue
Repairs must follow confirmed diagnosis and vary significantly by implementation.
If testing confirms a fuel injection pump controller failure on a diesel application, the pump may require replacement or professional recalibration.
Wiring repairs must be completed if harness damage or corrosion is found during the inspection.
If the coolant gauge circuit is confirmed faulty, repairing the damaged wiring or replacing the instrument cluster gauge motor typically resolves the issue.
If the immobilizer antenna coil fails testing, replacing the antenna ring and clearing the codes will restore the starting function.
Always clear the error code and perform a verification test drive or key cycle after any repair.
Cost Considerations for P1691 Repairs
Repair costs depend heavily on the underlying fault and the specific vehicle application.
Addressing a wiring issue or a poor connection is generally less expensive, primarily involving diagnostic time and minor materials.
Replacing an immobilizer antenna coil or an instrument cluster stepper motor involves moderate parts and labor costs.
Conversely, replacing a high-pressure diesel fuel injection pump and performing the necessary calibration is a major repair.
This diesel repair requires significant parts investment and specialized programming labor.
Prevention Strategies for Future Occurrences
Prevention strategies are tied to the specific failure mechanism of the affected system.
For diesel fuel systems, keeping the fuel filter clean and using high-quality diesel fuel can help protect the injection pump.
For gauge and immobilizer circuits, inspecting exposed wiring harnesses for chafing can help prevent moisture intrusion and corrosion.
Some electrical failures occur without warning and cannot be reliably prevented through routine maintenance.
Troubleshooting Tips and Best Practices
Always verify the exact manufacturer definition for P1691 before purchasing parts or beginning repairs.
Do not assume a fuel injection pump has failed solely based on the code without targeted circuit testing.
When diagnosing gauge circuits, avoid bypassing the instrument cluster, as this can disrupt the vehicle communication network.
Consult the exact manufacturer service information for your specific vehicle to ensure accurate diagnostic routines.
More OBD-II Codes
| P1689 | P1688 | P1687 | P1686 |
| P1685 | P1681 | P1692 | P1693 |
| P1694 | P1695 | P1702 | P1703 |
| P1684 | P1683 | P1682 | P1680 |
| P1602 | P1603 | P1604 | P1605 |
| P0700 | P0600 | P0601 | P0602 |
Frequently Asked Questions
Is P1691 a generic OBD-II code?
No. P1691 is a manufacturer-specific code, meaning its exact definition depends entirely on the vehicle make. It can indicate a fuel injection pump error, a coolant gauge circuit fault, or an immobilizer issue.
Can a P1691 code prevent my car from starting?
Yes, on certain Hyundai and Kia applications, P1691 indicates an immobilizer antenna coil error. If the immobilizer system cannot read the key transponder, the vehicle will crank but will not start.
Will disconnecting the battery clear a P1691 code?
Disconnecting the battery may temporarily clear the code, but it does not repair the underlying electrical fault. The code will likely return, and battery disconnection can erase valuable freeze-frame data needed for diagnosis.
Does P1691 always mean the fuel injection pump is bad?
No. While it indicates a calibration error on some diesel applications, wiring faults or corroded connectors can trigger the code. The injection pump should only be replaced after targeted circuit testing confirms internal failure.
Will a P1691 code turn on the check engine light?
MIL behavior varies by application. On vehicles where P1691 monitors the coolant gauge circuit or fuel injection pump, the check engine light typically illuminates. On some immobilizer applications, a dedicated security light may flash instead.
What Should You Do About the P1691 Code?
Confirm the exact factory definition for your specific vehicle before attempting any repairs.
Because P1691 is manufacturer-specific, testing the wrong system will waste time and money.
Follow the applicable manufacturer diagnostic procedure to inspect the relevant system and components, then repair or replace the confirmed failed part.
