1996 HONDA CIVIC 1 page

1.After the engine starts, the lAc valve opens for a certain time. The amount of air is increased to raise the idle speed
about 150 - 300 rpm.
When the coolant temperature is tow, the IAC valve is opened to obtain the proper fast idle speed. The amount of
bypassed air is thus controlled in relation to the engine coolant temperature'
IOLE SPEED
lrpml
176
80
ENGI ECOOLANI TEMPERATURE
t" Fl
toc)
ll
't.Whentheid|espeedisoutofspeciiicationandthescantoo|doesnotindicateDiagnosticTroub|ecode(DTc)P0505
or P1508. check the following items:
. Adiust the idle speed {see page 11-220}
. Starter switch signal (see page 11-202)
. Air conditioning signal (see page l1-204)
. ALT FR signal (see Page 11-2081
' Brake switch signal (see page 11-210)
. PSP switch signal (excapt Canada model) (see page 11-212)
. A,/T gear position signal {see section 14, Dl6Y5 engine (CVT):
page 11-216). Clutch switch signal (D16Y5 engine with M/T) (see page 11-218)
. Hoses and connections
' IAC valve and its mounting O-rings
lf the above items are normal, substitute a known-good IAC valve and readjust the idle speed (see page 11-220)
|ftheid|espeedsti||cannotbeadjustedtospecification(andthescantoo|doesnotindicateDTcP0505orP]50S)
after IAC valve replacement. substitute a known-good ECM/PCM and recheck. lf symptom goes away, replace the
original ECM/PCM.

ldle Control System
ldle ControlSystem
lF0505 l Th" """n tool indicates Diagnostic Trouble Code (DTC) PO5O5: tdte controt system malfunction.
NOTE: lf DTC P1508 or P1509 is stored at the same time as DTC P0505, troubleshoot DTC p1508 or p1bog first. thenrecheck for DTC P0505.
Possible Cause
. IAC valve mechanical malfunction
. Throttle body clogged pon, improper adjustment. Intake manifold gasket leakage
. Intake air hose loose leakage
. Vacu um leak
. ECT sensor incorrect output
. Throttle Position sensor incorrect output*r
Troubleshooting Flowchart
The MIL has been reoorted on.DTC P0505 is stored.
Problem verification:1. Start the engine. Hold theeng;ne at 3,000 rpm with noload (jn Park or neutral) untilthe radiator fan comes on, then*r let it idle.t2. with rhe scan toot, ct'eit Ge l
Throttle position should beapprox. 10% with the throttle fully closed.E ngine coolant tempera-ture should be 194 205'F(90 96.Ci.lf they are not within thespec., repair the faulty sen
L._ _9oI9[cr]41 l3. Chec& the engine speed atidle with no-load cond;tionsiheadlights, blower fan, reardefogger, radiator fan, and airconditioner are not operating\see page l1-22O - 223).
Intermittent tailure, system is OKat this time.ls the idle speed OK?
ls it 550 rpm or less?
(To page 11,193)
*1r'96 models only
11-192
(To page ll-193)

I
L
1D16Y5, D16Y8 engine with M/T 81642 engine)I
D16Y7 engine:
{From page 11-192)
Check the IAC valve:Disconnect the 3P connector from
the IAC valve.
Check the IAC valve:Disconnect the 2P connectorfrom the IAC valve.
Does the engine speed drop or
the engine stall?
Adiust the {base} idle speod (see
page 11-220 - 2231.It it's impos-
aible, clean the ports in lhe throt'
tle bodv,
(From page 11-192i
Check Ior vacuum leaks:1. Turn the ignition switch OFF.2. Remove the intake air ductfrom the throttle body.
3. Start the engine and let it idle.
4. Put your finger on the lowerpon in the th.ottle body.
Ch€ck tor vecuum loaks, m.kesure the throttle valve is com_pletaly closed, end repair as nec-Does the engine speed droP?
Adiust the idle speed (see page
11-220 - 2231. lf it's impossible,
reolace the IAC velve.UPPERPORT
1 1-1 93

ldle Control System
ldle Air Control (lACl Vatve ('96 - 98 Dl6ys, Dl6yB engine with M/Tl
The scan tool indicates Diagnostic Trouble Code (DTC) P1508: A problem in the ldle Air Controt flAC) varvecircuit.
The IAC Valve changes the amount of air bypassing the throttle body in response to a current signal from the ECM inorder to maintain the proper idle speed.
IAC VALVE 2P CONNECTOR ICl3A)
,flrcerh-:J iYEL/BLKI
!.__-,/ -lt(v)
-T-=
Wire side of female terminals
tAcv(BLK/
ELUI
ECM CONNECTOR A I32PI
Wire side oI lemal€ terminals
VALVE
6a10ll12t3r5t6l7t8t920232a
t*25&a2A3o
The MIL hss b€on repo.ted on.DTC P'l508 i. itorod.
Problem vorification:1. Do the ECM/PCM Reset Pro-cedure,Start the engine, and warm ituP to normal operating tem-perature.
Intormittont t!llur., sy.tcm b OKat thb tim6. Chsck fol poor con-ncctionr or loo3e wirot at C138(lAC valv.l.nd ECM.
ls DTC P1508 indicated?
Check for an opcn in the wiro(lGPl line):1. Turn the ignition switch OFF.2. Disconnect the IAC valve 2Pconnector.3. Turn the ignition switch ON (ll).
4. Measure vohage between bodyground and the IAC valve 2Pconnectorterminal No. 2.
R.prir opan in the wiro botwa.nIAC valv..nd PGM-FI main r.l.y.
Chock for an opon or sho in thewire (IACV linal:1. Turn the ignition switch OFFand reconnect the IAC valveconnector.2. Disconnect the ECM connectorA (32P).
3. Turn the ignit;on switch ON (ll).4. Measure voltage betweenbody ground and ECM con-nector terminal A12.
(To page 1l-195)
11-194

I
I
(From page 11-194)
Repair open or short in the wirebetween ECM lAl2l and IAC
Check the IAC valve Iunction:Momentarily connect ECM con-
nector terminals A12 and A10
with a jumPer wire several times.
Does the IAC valve click?
Substitute a known-good ECM
and recheck. It symPtom/indica-tion goes away, replace the origi-
nal ECM.
Wire side of female terminals

ldle Gontrol System
ldle Air Control (lAG) Valve ('99 - 00 Dl6Y8 engine with M/T, Bt6A2 enginel
[Fl50g l ]h" scan tool indicates Diagnostic Trouble Code (DTC) P1508: A problem in the ldle Air Controt AC) vatve- CtrCUtt.
The IAC Valve changes the amount of air bypassing the throttle body in response to a current signal from the ECM inorder to maintain the proper idle speed.
IAC VALVE 2P CONNECTOR IC138'
la rcprI - {YEL/8LKI 2t--d,
Y-=
Wire side ot female terminals
Wire side of lemale terminals
VALVE
The MIL has boon r€oorted on.DTC P1508 is srored.
Probl6m verification:1. Do the ECM/PCM Reset Pro-cedure.2. Start the engine, and warm itup to normal operating lem-perature.
Intermittent tailure, system is OKat this timg. Check to. poor con-noctions or loose wires at C138{lAC valvel and ECM.
ls DTC P1508 indicated?
Ch6ck for an open in the wir€{lGPl lino}:1. Turn the ignition switch OFF.2. Disconnect the IAC valve 2Pconnector.3. Turn the ignition switch ON (ll).
4. Measure voltage between bodyground and the IAC valve 2Pconneclor termina I No.2,
Repair opon in the wire bgtwoenIAC valve and PGM-Fl main relay.
Check tof an open or short in thewire {IACV line}l1. Turn the ignition switch OFFand reconnect the IAC valve
2. Disconnect the ECM connectorB {25P).3. Turn the ignition switch ON (ll).
4. Measure voltage betweenbody ground and ECM conn€ctor terminal 823.
(To page 11-197)
1 1-1 96

t
I
{From page 11-196)
Repair opon or short in lhe wire
between EcM lBzl) and lAc valve.ls there battery voltage?
Check the IAC valve fundion:Momentarily connect ECM con-
nector terminals 823 and 82 with
a iumpe. wire several tames.
Does the IAC valve click?
Substitute a known-good ECM
and rocheck. ll symptom/indicd-tion go€s away, rePlace tho origi_
nal ECM.
Wire side of female terminals
11-197

ldle Control System
ldle Air Control (lAC) Valve ('96 - 98 A/T and Dl6Y7 enginel
The (Rotary) IAC Valve changes the amount of air bypassing the throttle body in response to a current signal from theECM/PCM in order to maintain the proper idle speed,
BIMETAL
VALVESTOPPER
1P1509 Thescantool indicates Diagnostic Trouble Code (DTC) P1509: A problem in the idle Air Control (tAC)valve circuit.
ECM/PCM CONNECTOR A I32PIPGl IBLKI
IAC VALVE 3P CONNECIOR
IACV NIACV P
IGP
Terminal side of maleterminals
*: IACV N line
1 1-198
The MIL has b€€n roported on.DTC P1509 is stored.
Problem verification:1. Do the ECM/PCM Reset Proce-oure.2. Turn the ignition switch ON (ll).
Intermittent failura, systom ia OKat this time. Check tor poo. con-noctions or loose wires at C109llAC valve) and ECM/PCM.
ls DTC P1509 indicated?
Check for an opon in the wirer{PG lines):Measure voltage between bodvground and ECM/PCII connectorterminals A10 and A23 individu
Repair op€n in the wires betwoenECM/PCM and G101 llocated attho thermostat housing).
ls there more than 1.0 V?
Chock th€ ECM/PCM inpui volt-agel1. Turn the ignition switch OFF.2. Disconnect ECM/PCM connec-tor A (32P)from the ECM/PCM.3. Turn the ignition switch ON (ll).4. Measu re voltage betweenbody ground and ECM/PCMconnector terminals A14 andA13* individually.
Ch6ck th6 IAC valve:1. Turn the ignition switch OFF.2. Disconnect the IAC valve 3Pconnector,3, Measure resistance betweenIAC valve 3P connector termi-nal No.2 and terminals No. 1and 3 individually.
ls there 16 - 28 g?
Substitute a known-good ECM/PCM and recheck. lf symptom/indication goos away, replaceth€ origin.l ECM/PCM.
SHAFT
rAcv N loRNl*
(To page 11-199)
Wire side of lemale terminals
123a56El011
121314r5161718t9202:22321
272AA30
IACV P {BLK/BLUI