DTC 5-1-2
5-1-2 SHORT TERM FUEL TRIMTrouble Code Conditions
The Engine Control Module (ECM) receives information from the Heated Oxygen Sensor (HO2S) on the fuel/air mixture. If the fuel/air mixture deviates, the short term fuel trim will compensate for this by adjusting injection period. If the short term fuel trim remains lean for more than 3 minutes, and engine temperature exceeds 75°C (167°F), Diagnostic Trouble Code (DTC) 5-1-2 is set.
Substitute value(s)
- None.
Fault source(s)
- Faulty sensor signal.
- High fuel pressure.
Fault symptom(s)
- High fuel consumption.
- Uneven running.
TEST PROCEDURE
OTHER DTCS
- Read off other DTCs.
If DTC 1-2-1 is stored:
^ Fault trace DTC 1-2-1, Mass Air Flow (MAF) sensor signal.
If DTC 1-2-1 is not stored:
^ Check MAF sensor signal. Proceed to CHECK MAF SENSOR SIGNAL section below.
CHECK MAF SENSOR SIGNAL
- Start and warm up engine.
- Gear selector: neutral, A/C: off, engine warm.
- Power consumers such as engine coolant fan, heated rear window, etc.: off.
- Enter DTC parameter list.
- Read off load signal.
Value should read 2.3 - 2.4 volts at idle.
If value OK:
^ Check fuel pressure.
If fuel pressure OK:
^ Connect breakout box and check control points.
^ Check all signals on Motronic 1.8.
^ Fix as necessary.
^ Erase DTCs.
If value differs:
^ Check MAF sensor ground lead. Proceed to CHECK MAF SENSOR GROUND LEAD section below.
CHECK MAF SENSOR GROUND LEAD
- Ignition off.
- Disconnect MAF sensor.
- Connect an ohmmeter between MAF sensor connector contact 1 and ground.
Ohmmeter should read approx. 0 ohms.
If value OK:
^ Check MAF sensor connector for contact resistance and oxidation.
^ After fixing, check load signal. Proceed to CHECK LOAD SIGNAL section below.
If value differs:
^ Check connector. Proceed to CHECK CONNECTOR section below.
CHECK CONNECTOR
- Ignition off.
- MAF sensor disconnected.
- Check 55-pin connector in central relay unit (A3/E) connector 13 for contact resistance and oxidation.
- ECM connected.
- Connect an ohmmeter between MAF sensor connector contact 1 and ground.
Ohmmeter should read approx. 0 ohms.
If value OK:
^ Source of DTC is bad contact in connector.
If value differs:
^ Check lead between MAF sensor connector contact 1 and control point on engine (31/33) for break.
^ After fixing, check load signal. Proceed to CHECK LOAD SIGNAL section below.
CHECK LOAD SIGNAL
- Start and warm up engine.
- Gear selector: neutral, AC: off, engine warm.
- Power consumers such as engine coolant fan, heated rear window, etc.: off.
- Enter DTC parameter list.
- Read off load signal.
Value should read 2.3 - 2.4 volts at idle.
If value differs:
^ Test with a new MAF sensor.