MerCruiser 305 CID (5.0L) Service Manual page 687

DIAGNOSTICS
Code 21 (3 of 3): Throttle Position (TP) Sensor Circuit
Step
9.
10. 10.
11. 11.
12.
13.
14.
15.
16.
17.
18.
Index
Page 5G-60
a. Ignition OFF.
b. Connect a test light to battery positive (B+).
c. Touch test light to harness terminal "C" (throttle position
sensor signal).
Is test light on?
Connect DVOM between harness terminal "C" and
engine ground (–).
Is voltage reading over 4 volts?
Connect DVOM from throttle position sensor harness ter-
minal "A" to a good ground on engine.
Is voltage reading over 4 volts?
a. Disconnect ECM.
b. Touch test light to harness terminal "C" (throttle position
sensor signal).
Is test light on?
Check for CKT 417 shorted to voltage.
Locate and repair open in CKT 417 or faulty connection
at ECM.
Replace throttle position sensor.
Check for CKT 417 shorted to ground.
CKT 416 open or shorted to ground or faulty connection
at ECM.
CKT 813 open faulty connection at ECM.
Action
SERVICE MANUAL NUMBER 24
Yes No
PROCEED TO
Step 12. Step 15.
Step 13. Step 14.
Step 18. Step 17.
Step 16. Step 14.
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90-861327--1 OCTOBER 1999