SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSAUDI1996A4 BASE, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODES - 2.8LCIRCUIT TESTSDTC P0174/16558 - SYSTEM TOO LEAN (BANK 2)
1996 Audi A4 Base, Standard

DTC P0174/16558 - System Too Lean (Bank 2)

1996 Audi A4 Base, StandardSECTION DTC P0174/16558 - System Too Lean (Bank 2)
NOTE: DTC is set when HO2S control has exceeded the learning limit in rich direction, but HO2S still recognizes mixture is too lean.
  1. Bank 1 identifies fuel injectors on passenger side of engine. If DTC P0171/16555 SYSTEM TOO LEAN (BANK 1) is also set in memory, this indicates a condition is present causing both cylinder banks to run too lean. Go to step 7). If DTC P0171/16555 is not also set in memory, go to next step.
  2. Inspect exhaust system on driver side of vehicle for a leak. Repair as necessary. If an exhaust leak was not found, go to next step. If an exhaust leak was repaired, erase DTC memory and test drive vehicle.
  3. Inspect air intake system for a leak. Repair as necessary. If an intake leak was not found, go to next step. If an intake leak was repaired, erase DTC memory and test drive vehicle.
  4. Inspect spark plugs and ignition cables for malfunction on driver side of vehicle. If a malfunction was not repaired, go to next step. If a malfunction was repaired, erase DTC memory and test drive vehicle.
  5. Inspect fuel injectors on driver side of vehicle for poor electrical connection or dirty/clogged injectors. See FUEL INJECTOR TEST in BASIC TESTING article. If a malfunction was not repaired, go to next step. If a malfunction was repaired, erase DTC memory and test drive vehicle.
  6. Inspect intake valves for carbon deposits. Clean as necessary. If intake valves did not have carbon deposits, continue troubleshooting other DTCs. See DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION  table. If intake valves had carbon deposits, erase DTC memory and test drive vehicle.
  7. If DTC P1250/17658 FUEL LEVEL TOO LOW is also set in memory, this indicates there is less than 12.7 qts. (12 L) of fuel in tank. Check fuel tank level and fill if necessary. If fuel level is okay, go to next step. If fuel level was low, erase DTC memory and test drive vehicle.
  8. Inspect air intake system for a large leak. Repair as necessary. If a large intake leak was not found, go to next step. If a large intake leak was repaired, erase DTC memory and test drive vehicle.
  9. DTC may have been set because of low fuel pressure. Inspect fuel lines for leaks. Inspect vacuum line to fuel pressure regulator. Inspect fuel pressure regulator. Inspect fuel filter. Inspect fuel pump. See FUEL PUMP table. Repair as necessary. If components are okay, go to next step. If a malfunction was repaired, erase DTC memory and test drive vehicle.
    FUEL PUMP PERFORMANCE

    Function Specification
    System Pressure
    With Engine Idling (1) 55-61 psi (3.8-4.2 bar)
    With Engine Idling (Warm) (2) 46-55 (3.2-3.8 bar)
    Residual Pressure
    Engine Cold (3) 32 psi (2.2 bar)
    Engine Hot (3) 44 psi (3.0 bar)
    Fuel Injector/Injection Rate (4) 2.9-3.7 oz. (86-109 ml)
    (1) With fuel pressure regulator vacuum hose disconnected.
    (2) With fuel pressure regulator vacuum hose connected.
    (3) After 10 minutes.
    (4) Per 30 seconds of operation.
  10. Disconnect EVAP canister purge valve electrical connector. Using DVOM, check EVAP canister purge valve resistance. Measure resistance across EVAP canister purge valve terminals. Resistance should be 20-28 ohms. If resistance is within specification, go to next step. If resistance is not with specification, replace EVAP canister purge valve. Erase DTC memory and test drive vehicle.
  11. With ignition on, connect VAG 1527B voltage tester between EVAP canister purge valve harness connector terminal No. 1 and ground. Voltage tester should light up. If voltage tester lights up, go to next step. If voltage tester does not light up, check fuse for EVAP canister purge valve. If fuse is okay, go to next step. If fuse was replaced, erase DTC memory and test drive vehicle.
  12. Using a DVOM, check wiring between EVAP canister purge valve harness connector terminal No. 1 and fuse. See WIRING DIAGRAMS  section. If wiring is okay, check fuel pump relay and relay triggering. See SYSTEM/COMPONENT TESTS article. Go to next step.
  13. Connect VAG 1527B voltage tester between EVAP canister purge valve harness connector terminals. Using VAG 1551 scan tool, use OUTPUT DIAGNOSTIC TEST mode, function 03 to trigger EVAP canister purge valve. Voltage tester should flash. If voltage tester does not flash or lights up continuously, go to next step. If voltage tester flashes, ensure EVAP canister purge valve is not mechanically binding. Replace as necessary. Erase DTC memory and test drive vehicle.
  14. Turn ignition off. Disconnect Powertrain Control Module (PCM) connectors. Connect VAG 1598/19 test box to PCM wiring harness. Terminal assignments of test box are identical to PCM connectors "A", "B", "C", "D" and "E".
  15. If voltage tester had lit up constantly, go to step 18). If voltage tester did not flash, using DVOM, check resistance between EVAP canister purge valve harness connector terminal No. 2 and test box socket E12. Maximum resistance is one ohm. If resistance is not within specification, go to next step. If resistance is within specification, circuit resistance is okay. Go to step 17).
  16. Repair open circuit as necessary. Erase DTC memory and test drive vehicle. If open circuit cannot be located, replace faulty PCM. Code new PCM and test drive vehicle. See PCM CODING  in this article.
  17. Using DVOM, check for short to B+ between EVAP canister purge valve harness connector terminal No. 2 and test box socket E12. If short to B+ is present, repair as necessary. Erase DTC memory and test drive vehicle. If short to B+ cannot be located, replace faulty PCM. Code new PCM and test drive vehicle. See PCM CODING  in this article.
  18. Using DVOM, check for a short to ground between EVAP canister purge valve harness connector terminal No. 2 and test box socket E12. If a short to ground is not present, circuit is okay. Replace faulty PCM. Code new PCM and test drive vehicle. Refer to PCM CODING  in this article. If a short to ground is present, repair as necessary. Erase DTC memory and test drive vehicle.
RENDER: 1.0x

NO RELATED

Recommended Tools & Savings

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Affiliate disclosure: We may earn a commission at no extra cost to you.

Shop Manual-Ready ToolsFree Quote CheckQuote Shield Pro

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.