Fix P0193: Mechanic’s solutions that WORKED

The code P0193: Fuel Rail Pressure Sensor Circuit High Input points out a fault in the fuel system, specifically indicating that the fuel rail pressure sensor circuit is receiving a higher voltage than expected. This can be caused by a faulty sensor, wiring issues, or problems within the fuel system affecting pressure readings.

P0193 quick overview

Meaning	P0193: Fuel Rail Pressure Sensor Circuit High Input
Is it serious?	This code can be serious as it relates to the engine’s fuel system and can affect the vehicle’s performance, potentially leading to stalling or poor running conditions.
Possible causes	– Faulty fuel rail pressure sensor – Pinched or damaged wiring harness – Corrosion or poor connections at the sensor or ECM – Faulty 5-volt reference from ECM – Issues with the fuel pump or fuel pressure regulator
How to diagnose?	Check FRP Sensor: Inspect the fuel rail pressure sensor for damage or signs of failure. Inspect Wiring: Look for pinched, damaged, or corroded wires, especially around the alternator bracket or other tight areas. Verify Grounds: Ensure all ground connections are secure and clean. Test 5V Reference: Check the 5V reference circuit from the ECM to ensure it’s not shorted. Load Test Circuits: Perform a load test on relevant circuits to check for voltage drops. Wiggle Test: Wiggle wiring and connectors while monitoring sensor readings for changes.

How to fix P0193 – learn from mechanics

I looked into P0193 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Lexus

Vehicle Information:
2006 Lexus GS300 3.0L

Issue + Repair History:

• MIL on with code P0193 for fuel rail pressure sensor high input.
• Vehicle has only 19k miles and looks clean.
• Confirmed the sensor and three wires are connected and within spec.

Other OBD2 Codes + Test Results:

• P0193: Fuel rail pressure sensor circuit high input

Suggestions to Fix Issue:

• Check for bad connections or open circuits as they often cause high input signals.
• Look for TSBs or recalls related to this issue and consult with a Lexus dealer.
• Consider that the fuel pressure sensor has likely failed if wiring is intact.
• Replace the sensor if pin fitment is good and other diagnostics confirm its failure.

Final Fix:
The fuel pressure sensor attached to the rear end of the fuel rail was faulty and replacing it resolved the issue.

Case #2: Ford

Vehicle Information:
2004 Ford Freestar SES 3.9L

Issue + Repair History:

• Experienced hesitation, bucking, jerking, and stalling.
• Initial code P0193, which disappeared after replacing the fuel rail pressure sensor.
• New code P0191 appeared after test drive.
• Replaced plugs, wires, coil, and FRP sensor.
• Issues persisted, especially on cold take-off.
• Fuel pressure did not drop but increased to 50 psi during stalling.

Other OBD2 Codes + Test Results:

• P0191: Fuel rail circuit performance
• P0193: FRP sensor circuit high input (resolved after sensor replacement)
• P1233: Fuel pump driver module offline

Suggestions to Fix Issue:

• Consider replacing the coolant temp sensor for cold start issues.
• Check fuel pump health, especially if the vehicle is often run low on fuel.
• Investigate for a partially blocked injector or a bad fuel pump.
• Inspect the PCM for water damage or corrosion, especially in the connector pins.

Final Fix:

• Performed a 60k service, including all fluids/filters.
• Replaced fuel rail sensor for the first code and fuel pump for the secondary code.
• Removed and resealed PCM for TSB inspection; found and addressed minor moisture.
• Reset KAM memory and erased codes; no problems since (~1k miles & 1 week later).

Case #3: Chevrolet

Vehicle Information:
2005 Chevrolet C5500 Kodiak C5C042 6.6L

Issue + Repair History:

• MIL on with codes P0193 and P0670.
• Idles fine but will not drive.
• Previously found a shorted wire behind the alternator bracket.
• Checked all wiring and followed flow charts for each code.
• Replaced the engine earlier.

Other OBD2 Codes + Test Results:

• P0193: Fuel Rail Pressure sensor circuit high
• P0670: Glow plug Module control
• Fuel rail pressure reading 26,106 psi with the engine not running.

Suggestions to Fix Issue:

• Focus on the abnormal 26K pressure reading, likely due to a sensor or wiring issue.
• Check if the fuel pressure sensor is bad or if there’s a wiring problem to it.
• Ensure glow plugs are operational and check their resistance and if they can be commanded on.
• Verify all connections to the glow plug module and check for any blown fuses.

Final Fix:
After extensive diagnostics and consultation, the vehicle was taken to a diesel shop. The dealer identified a bad fuel pressure sensor as the problem.

Case #4: Ford

Vehicle Information:
2006 Ford E-350 Super Duty 5.4L

Issue + Repair History:

• Consistently getting P0193 and P0670 codes.
• Experiences hesitation, stalling, and poor performance but idles fine.
• Replaced fuel pump two months prior for no start issue.
• Replaced fuel rail pressure/temp sensor several times.

Other OBD2 Codes + Test Results:

• P0193: Fuel rail pressure sensor circuit too high
• P0670: Glow plug Module control

Suggestions to Fix Issue:

• Consider the possibility of a bad run of OEM parts and try a used or aftermarket sensor.
• Replace the fuel rail pressure sensor wiring harness connector.
• Check wiring for internal corrosion or faulty ground, and perform a load test.
• Inspect the ground on the right side frame rail to the body, especially in areas with heavy rust.
• Conduct a wiggle test on the wiring to check for breaks inside the insulation.
• Verify voltage measurements at the fuel pump and consider potential issues with the wiring to the Fuel Pump Control Module (FPCM).
• Check for any chafing or damage to the wiring harness, especially near heat sources like the EGR feed tube.

Final Fix:

• After multiple sensor replacements failed, an old sensor from a police interceptor was used and it resolved the issue.
• Concluded that the new sensors might lack quality control.
• Performed a 60k service, replaced the fuel rail sensor for the first code, and the fuel pump for the secondary code.
• Resealed and dried the PCM after finding minor moisture, which appeared to resolve hesitation issues.
• No problems reported after about 1k miles and one week.

Case #5: Chevrolet

Vehicle Information:
2005 Chevrolet C5500 Kodiak C5C042 6.6L

Issue + Repair History:

• No start issue after replacing the oil pump.
• Initially had codes P0193 and P0642.
• Replaced engine harness due to pinch damage.
• Rusty transmission line leaking at the transmission.

Other OBD2 Codes + Test Results:

• P0193: Fuel Rail Pressure Sensor Circuit High
• P0642: 5 Volt Reference 1 Circuit Low
• U0106: Lost Communication with Glow Plug Control Module

Suggestions to Fix Issue:

• Check for broken or missing grounds.
• Download wiring diagrams and trace circuits related to the codes.
• Address the 5V reference code first as it might fix the fuel rail code.
• Wiggle ECM and IDM connectors while trying to start the engine.
• Check for harness pinched behind the alternator bracket on the LH side of the engine.
• Monitor the 5V reference parameters and wiggle the harness to restore/change the value.
• Look for loose connector pins or a pinched wire.
• Consider the possibility that the wiring to the oil sensor is shorted, causing the P0193 and no start.

Final Fix:

• After extensive diagnostics, discovered the engine harness was pinched, causing the 5V reference issue and subsequent codes.
• Replacing the pinched harness resolved the no-start issue and cleared the codes.
• Addressed a rusty transmission line that was leaking at the transmission.

Advice	Diagnostic Step Description
Check for Pinched Wires	Inspect the harness for areas where wires might be pinched, particularly behind the alternator bracket or near other tight spots.
Inspect Ground Connections	Ensure all ground connections are secure and clean, especially ones that were removed during recent repairs.
Verify 5V Reference	Check the 5V reference circuit for integrity and ensure it’s not shorted to ground or power, which could affect sensor readings.
Replace the FRP Sensor	If the fuel rail pressure sensor is repeatedly failing or showing erratic readings, consider replacing it.
Check for Wiring Corrosion and Damage	Inspect the wiring and connectors for signs of corrosion, damage, or poor pin fit, especially at the fuel pressure sensor and ECM.
Load Test Circuits	Perform a load test on relevant circuits to ensure they can handle the current without voltage drops that could cause incorrect readings.
Wiggle Test Wiring and Connectors	While monitoring sensor readings, wiggle the wiring and connectors to check for changes that might indicate a poor connection or damaged wire.