DTC 20

Fig. 15 Fuel Pump & Injector Wiring Circuit:

When the ignition switch is turned On, fuel pump circuit 120 should indicate 12 volts, then zero volts after a period of one second. The fuel pump circuit should apply 12 volts to the fuel pump with the engine running. Code 20 indicates that the fuel pump relay circuit did not supply 12 volts to the fuel pump. Possible causes of this condition are:
a. Defective fuel pump relay.
b. Defective wiring harness or electrical connectors.
c. ECM not processing fuel pump signal or not turning fuel pump relay on.
d. A short circuit inside fuel pump.
To diagnosis a Code 20, proceed as follows:
1. Turn ignition off for 10 seconds, then turn on for 5 seconds and attempt to start engine.
2. If engine starts with Code 20 stored as an intermittent, there is no malfunction in the system at this time. If an intermittent Code 20 is being set, display parameter .1.0 with engine running, disconnect oil pressure switch, then manipulate related wiring. If the failure is now induced, battery voltage reading will drop from its normal reading to 0 volts. This will help to isolate location of malfunction.
3. If engine starts with Code 20 stored as a hard code, proceed as follows:
a. With engine running, enter diagnostics and display parameter .1.0.
b. If parameter .1.0 is 0 volts, check circuit 120 to ECM for an open. If circuit is satisfactory, check ECM or ECM connector for a fault and repair or replace as necessary.
c. If parameter .1.0 reads battery voltage, proceed to step 4b of this procedure.
4. If engine will not start, proceed as follows:
a. Inspect 10 amp fuel pump fuse. If fuse is blown, proceed to step 5 of this procedure.
b. If fuse is not blown, turn ignition off for 10 seconds and remove fuel pump relay.
c. Connect test lamp between fuel pump relay cavity 5 and ground, then turn ignition on.
d. If test lamp does not light, reinstall fuel pump relay and check circuit 465 for an open or short to ground. If circuit and relay are satisfactory, check for faulty ECM or ECM connector and repair or replace as necessary. If relay or circuit is defective, make necessary repairs.
e. If test lamp in step 4c remains lit for 2 seconds, reconnect test lamp between fuel pump relay cavity 1 and ground. If test lamp does not light with ignition on, repair open in circuit 120F or 3. If test lamp lights, reconnect lamp between relay cavities 1 and 2.
f. If test lamp between cavities 1 and 2 does not light with ignition on, check circuit 497 for an open and repair as necessary. If circuit is satisfactory, check for faulty ECM or ECM connector and repair or replace as necessary.
g. If test lamp between cavities 1 and 2 lights with ignition on, reconnect lamp between cavities 1 and 4. If test lamp lights with ignition on, replace fuel pump relay. If lamp does not light, repair open in circuit 120E.
5. If fuel pump fuse is blown, proceed as follows:
a. Remove fuel pump relay and connect test lamp between fuel pump relay cavity 4 and 12 volt power source.
b. Turn ignition on, enter diagnostics and display parameter 10. If value of parameter 10 is more than 0 volts, proceed to step 5c. If value of parameter is 0 volts, proceed to step 5e.
c. Connect test lamp between relay cavity 1 and 12 volt power source. If test lamp does not light, replace fuel pump relay. If test lamp lights, proceed to step 5d.
d. Disconnect oil pressure switch electrical connector and observe test lamp. If lamp remains lit, repair short to ground in circuit 120F. If lamp does not light, replace oil pressure switch.
e. Disconnect electrical connector at fuel tank and note parameter value. If value of parameter is 0 volts, proceed to step 5f. If value is more than 0 volts, proceed to step 5g.
f. Disconnect oil pressure switch and note parameter value. If value remains 0 volts, repair short to ground in circuit 120 or 120E. If value is now more than 0 volts, replace oil pressure switch.
g. Check circuit 120 from electrical connector at fuel tank to fuel pump for a short to ground and repair as necessary. If circuit is satisfactory, inspect fuel pump for a short to ground and repair as necessary.