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Home / DTC / P0091 — Fuel Pressure Regulator A Control Circuit Low

P0091 — Fuel Pressure Regulator A Control Circuit Low

Detailed page for trouble code P0091.

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22,461specific
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Code

P0091

Generic P — Powertrain

Fuel Pressure Regulator A Control Circuit Low

Brand: Generic
Type: P — Powertrain
Views: UK: 36 EN: 82 RU: 54
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Short to ground on the regulator control circuit
  • Open or high resistance in wiring or connector to the fuel pressure regulator
  • Faulty fuel pressure regulator (solenoid/coils)
  • PCM/ECM driver fault or internal short
  • Corroded/loose connectors or terminal damage
  • Aftermarket modifications or incorrect replacement parts

Symptoms

  • Check engine MIL illumination with P0091 stored
  • Hard starting or extended cranking
  • Engine hesitation, poor acceleration or stumbling under load
  • Fuel trim abnormalities (high or low short-term/long-term fuel trims)
  • Abnormal fuel rail pressure (too low or unstable)
  • Possible rough idle

What to check

  • Retrieve freeze frame and live data with a scan tool (commanded regulator duty/voltage and actual fuel rail pressure)
  • Visual inspection of regulator connector and wiring harness for corrosion, damage, or pin push-out
  • Backprobe regulator control connector and measure voltage with key on/engine running
  • Measure coil resistance of the fuel pressure regulator (compare to manufacturer spec)
  • Inspect related fuel system fuses, relays and ground points
  • Perform wiggle test of harness while monitoring signal for intermittent faults

Signal parameters

  • Expected control signal: 0–5 V or PWM duty 0–100% (varies by manufacturer)
  • Low condition: near 0 V or 0% duty when PCM expects higher voltage/duty
  • Typical regulator coil resistance (generic): ~5–35 ohms — check OEM spec
  • Fuel rail pressure example (gasoline port-injection): ~40–60 psi — use OEM specification for exact values

Diagnostic algorithm

  1. Read and record DTCs and freeze-frame data. Clear codes and attempt to reproduce.
  2. Using a scan tool, observe commanded regulator output (voltage or duty) and actual fuel rail pressure while repeating failure conditions.
  3. With ignition ON (engine off) backprobe the regulator control pin: verify voltage matches scan tool commanded value. If signal is low when PCM commands higher, suspect wiring/short or PCM.
  4. Disconnect regulator connector and measure resistance between control terminal and ground. If short to ground persists with connector disconnected, trace wiring for short to ground.
  5. Check for voltage supply (if high-side supply is used) and for any fused circuits feeding the regulator. Repair any open or poor power feeds.
  6. Measure coil resistance of the regulator at the connector; if out of spec, replace regulator.
  7. If wiring and regulator check good, perform PCM output test per manufacturer procedure or substitute known-good PCM if available. Do not replace PCM without confirming the circuit wiring and load are good.
  8. After repairs, clear codes and verify proper operation with road test and scan tool monitoring of fuel pressure and regulator command.

Likely causes

  • Damaged wiring insulation chafing to chassis ground
  • Corroded connector pins at regulator or harness connector
  • Failed regulator coil with internal short to ground
  • PCM driver transistor failure (low output)

Fault status

⚠️ Status
Control circuit for Fuel Pressure Regulator A is reporting a voltage/signal lower than expected (low). Possible cause: short to ground, regulator fault, wiring/connectors, or PCM driver issue.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

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Code

P0091

ISUZU P — Powertrain

Fuel Pressure Regulator Control Circuit Low

Brand: ISUZU
Type: P — Powertrain
Views: UK: 28 EN: 124 RU: 83
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Short to ground on the regulator control circuit
  • Open or high resistance in wiring or connector to the fuel pressure regulator
  • Faulty fuel pressure regulator (solenoid/coils)
  • PCM/ECM driver fault or internal short
  • Corroded/loose connectors or terminal damage
  • Aftermarket modifications or incorrect replacement parts

Symptoms

  • Check engine MIL illumination with P0091 stored
  • Hard starting or extended cranking
  • Engine hesitation, poor acceleration or stumbling under load
  • Fuel trim abnormalities (high or low short-term/long-term fuel trims)
  • Abnormal fuel rail pressure (too low or unstable)
  • Possible rough idle

What to check

  • Retrieve freeze frame and live data with a scan tool (commanded regulator duty/voltage and actual fuel rail pressure)
  • Visual inspection of regulator connector and wiring harness for corrosion, damage, or pin push-out
  • Backprobe regulator control connector and measure voltage with key on/engine running
  • Measure coil resistance of the fuel pressure regulator (compare to manufacturer spec)
  • Inspect related fuel system fuses, relays and ground points
  • Perform wiggle test of harness while monitoring signal for intermittent faults

Signal parameters

  • Expected control signal: 0–5 V or PWM duty 0–100% (varies by manufacturer)
  • Low condition: near 0 V or 0% duty when PCM expects higher voltage/duty
  • Typical regulator coil resistance (generic): ~5–35 ohms — check OEM spec
  • Fuel rail pressure example (gasoline port-injection): ~40–60 psi — use OEM specification for exact values

Diagnostic algorithm

  1. Read and record DTCs and freeze-frame data. Clear codes and attempt to reproduce.
  2. Using a scan tool, observe commanded regulator output (voltage or duty) and actual fuel rail pressure while repeating failure conditions.
  3. With ignition ON (engine off) backprobe the regulator control pin: verify voltage matches scan tool commanded value. If signal is low when PCM commands higher, suspect wiring/short or PCM.
  4. Disconnect regulator connector and measure resistance between control terminal and ground. If short to ground persists with connector disconnected, trace wiring for short to ground.
  5. Check for voltage supply (if high-side supply is used) and for any fused circuits feeding the regulator. Repair any open or poor power feeds.
  6. Measure coil resistance of the regulator at the connector; if out of spec, replace regulator.
  7. If wiring and regulator check good, perform PCM output test per manufacturer procedure or substitute known-good PCM if available. Do not replace PCM without confirming the circuit wiring and load are good.
  8. After repairs, clear codes and verify proper operation with road test and scan tool monitoring of fuel pressure and regulator command.

Likely causes

  • Damaged wiring insulation chafing to chassis ground
  • Corroded connector pins at regulator or harness connector
  • Failed regulator coil with internal short to ground
  • PCM driver transistor failure (low output)

Fault status

⚠️ Status
Control circuit for Fuel Pressure Regulator A is reporting a voltage/signal lower than expected (low). Possible cause: short to ground, regulator fault, wiring/connectors, or PCM driver issue.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0090 P0092 P0087 P0088 P0191 P0193
Repair manuals

Manual library for ISUZU

86

Browse 86 ISUZU manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

ISUZU

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Code

P0091

LAND ROVER P — Powertrain

Pressure regulator control of fuel - low circuit

Brand: LAND ROVER
Type: P — Powertrain
Views: UK: 14 EN: 67 RU: 43
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Short to ground on the regulator control circuit
  • Open or high resistance in wiring or connector to the fuel pressure regulator
  • Faulty fuel pressure regulator (solenoid/coils)
  • PCM/ECM driver fault or internal short
  • Corroded/loose connectors or terminal damage
  • Aftermarket modifications or incorrect replacement parts

Symptoms

  • Check engine MIL illumination with P0091 stored
  • Hard starting or extended cranking
  • Engine hesitation, poor acceleration or stumbling under load
  • Fuel trim abnormalities (high or low short-term/long-term fuel trims)
  • Abnormal fuel rail pressure (too low or unstable)
  • Possible rough idle

What to check

  • Retrieve freeze frame and live data with a scan tool (commanded regulator duty/voltage and actual fuel rail pressure)
  • Visual inspection of regulator connector and wiring harness for corrosion, damage, or pin push-out
  • Backprobe regulator control connector and measure voltage with key on/engine running
  • Measure coil resistance of the fuel pressure regulator (compare to manufacturer spec)
  • Inspect related fuel system fuses, relays and ground points
  • Perform wiggle test of harness while monitoring signal for intermittent faults

Signal parameters

  • Expected control signal: 0–5 V or PWM duty 0–100% (varies by manufacturer)
  • Low condition: near 0 V or 0% duty when PCM expects higher voltage/duty
  • Typical regulator coil resistance (generic): ~5–35 ohms — check OEM spec
  • Fuel rail pressure example (gasoline port-injection): ~40–60 psi — use OEM specification for exact values

Diagnostic algorithm

  1. Read and record DTCs and freeze-frame data. Clear codes and attempt to reproduce.
  2. Using a scan tool, observe commanded regulator output (voltage or duty) and actual fuel rail pressure while repeating failure conditions.
  3. With ignition ON (engine off) backprobe the regulator control pin: verify voltage matches scan tool commanded value. If signal is low when PCM commands higher, suspect wiring/short or PCM.
  4. Disconnect regulator connector and measure resistance between control terminal and ground. If short to ground persists with connector disconnected, trace wiring for short to ground.
  5. Check for voltage supply (if high-side supply is used) and for any fused circuits feeding the regulator. Repair any open or poor power feeds.
  6. Measure coil resistance of the regulator at the connector; if out of spec, replace regulator.
  7. If wiring and regulator check good, perform PCM output test per manufacturer procedure or substitute known-good PCM if available. Do not replace PCM without confirming the circuit wiring and load are good.
  8. After repairs, clear codes and verify proper operation with road test and scan tool monitoring of fuel pressure and regulator command.

Likely causes

  • Damaged wiring insulation chafing to chassis ground
  • Corroded connector pins at regulator or harness connector
  • Failed regulator coil with internal short to ground
  • PCM driver transistor failure (low output)

Fault status

⚠️ Status
Control circuit for Fuel Pressure Regulator A is reporting a voltage/signal lower than expected (low). Possible cause: short to ground, regulator fault, wiring/connectors, or PCM driver issue.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0090 P0092 P0087 P0088 P0191 P0193
320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

LAND ROVER

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
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