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  <xs:element id="psix_TransportationEndMarketMember" abstract="true" name="TransportationEndMarketMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_NorthAmericaExcludingUnitedStatesMember" abstract="true" name="NorthAmericaExcludingUnitedStatesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_PacificRimMember" abstract="true" name="PacificRimMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_OtherGeographicalAreasMember" abstract="true" name="OtherGeographicalAreasMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_ContractWithCustomerAssetLiability" abstract="false" name="ContractWithCustomerAssetLiability" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_ShareholdersLoanAgreementWeichaiMember" abstract="true" name="ShareholdersLoanAgreementWeichaiMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_CollaborativeArrangementTerm" abstract="false" name="CollaborativeArrangementTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="psix_CollaborativeArrangementInventoryPurchasedGoods" abstract="false" name="CollaborativeArrangementInventoryPurchasedGoods" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour" abstract="false" name="FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_ScheduleOfLongTermDebtAndShortTermDebtInstrumentsTable" abstract="true" name="ScheduleOfLongTermDebtAndShortTermDebtInstrumentsTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="psix_ScheduleOfLongTermDebtAndShortTermDebtInstrumentsLineItems" abstract="true" name="ScheduleOfLongTermDebtAndShortTermDebtInstrumentsLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="psix_FinanceLeaseLiabilityAndOtherLongTermDebt" abstract="false" name="FinanceLeaseLiabilityAndOtherLongTermDebt" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_LongTermDebtExcludingNotesPayable" abstract="false" name="LongTermDebtExcludingNotesPayable" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_RevolvingCreditAgreementInEventMajorityShareholderHoldsLessThan50OfEquityMember" abstract="true" name="RevolvingCreditAgreementInEventMajorityShareholderHoldsLessThan50OfEquityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_FourthAmendedAndRestatedCreditAgreementMember" abstract="true" name="FourthAmendedAndRestatedCreditAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_PreviousShareholderLoanAgreementsWeichaiMember" abstract="true" name="PreviousShareholderLoanAgreementsWeichaiMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_DebtInstrumentIncrementalBorrowingCost" abstract="false" name="DebtInstrumentIncrementalBorrowingCost" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="psix_DebtInstrumentAmountNotSubjectToSubordination" abstract="false" name="DebtInstrumentAmountNotSubjectToSubordination" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_DebtInstrumentMajorityShareholderOwnershipThresholdForVariableRateIncrease" abstract="false" name="DebtInstrumentMajorityShareholderOwnershipThresholdForVariableRateIncrease" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="psix_LongTermDebtExcludingNotesPayableMember" abstract="true" name="LongTermDebtExcludingNotesPayableMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_DebtInstrumentOptionalFaceAmount" abstract="false" name="DebtInstrumentOptionalFaceAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_MaturitiesOfLongTermDebtDiscountAmortizationAbstract" abstract="true" name="MaturitiesOfLongTermDebtDiscountAmortizationAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="psix_AmortizationOfDebtDiscountPremiumYearOne" abstract="false" name="AmortizationOfDebtDiscountPremiumYearOne" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_AmortizationOfDebtDiscountPremiumYearTwo" abstract="false" name="AmortizationOfDebtDiscountPremiumYearTwo" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_AmortizationOfDebtDiscountPremiumYearThree" abstract="false" name="AmortizationOfDebtDiscountPremiumYearThree" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_LeaseCostExcludingSubleaseIncome" abstract="false" name="LeaseCostExcludingSubleaseIncome" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_CashFlowLesseeAbstract" abstract="true" name="CashFlowLesseeAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="psix_RightOfUseAssetObtainedInExchangeForLeaseLiabilityAbstract" abstract="true" name="RightOfUseAssetObtainedInExchangeForLeaseLiabilityAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="psix_OperatingLeaseAssetsAndLiabilitiesLesseeAbstract" abstract="true" name="OperatingLeaseAssetsAndLiabilitiesLesseeAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="psix_FinanceLeaseAssetsAndLiabilitiesLesseeAbstract" abstract="true" name="FinanceLeaseAssetsAndLiabilitiesLesseeAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="psix_JeromeTreadwellv.TheCompanyMember" abstract="true" name="JeromeTreadwellv.TheCompanyMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_MastPowertrainV.TheCompanyMember" abstract="true" name="MastPowertrainV.TheCompanyMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_GaryWinemasterVersusTheCompanyMember" abstract="true" name="GaryWinemasterVersusTheCompanyMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_InsuranceCarrierMember" abstract="true" name="InsuranceCarrierMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_LossContingencyDamagesSoughtValuePerNegligentViolation" abstract="false" name="LossContingencyDamagesSoughtValuePerNegligentViolation" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_LossContingencyDamagesSoughtValuePerIntentionalViolation" abstract="false" name="LossContingencyDamagesSoughtValuePerIntentionalViolation" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_LossContingencyStayCaseTerm" abstract="false" name="LossContingencyStayCaseTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="psix_NumberOfOutstandingLettersOfCredit" abstract="false" name="NumberOfOutstandingLettersOfCredit" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="psix_ResearchAndDevelopmentAndStateTaxCreditCarryforwardMember" abstract="true" name="ResearchAndDevelopmentAndStateTaxCreditCarryforwardMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_DeferredTaxAssetsOperatingLeaseLiability" abstract="false" name="DeferredTaxAssetsOperatingLeaseLiability" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_DeferredTaxAssetsTaxCreditCarryforwardsOtherState" abstract="false" name="DeferredTaxAssetsTaxCreditCarryforwardsOtherState" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_DeferredTaxLiabilitiesIntangibleAmortization" abstract="false" name="DeferredTaxLiabilitiesIntangibleAmortization" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_PreferredStockSeriesAuthorized" abstract="false" name="PreferredStockSeriesAuthorized" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="psix_ShareBasedPaymentArrangementNumberOfSharesReceivedShareOfCommonStock" abstract="false" name="ShareBasedPaymentArrangementNumberOfSharesReceivedShareOfCommonStock" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="psix_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisableNumber" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisableNumber" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="psix_SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageExercisePrice" abstract="false" name="SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageExercisePrice" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="psix_SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionEquityInstrumentsGrantsInPeriodWeightedAverageExercisePrice" abstract="false" name="SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionEquityInstrumentsGrantsInPeriodWeightedAverageExercisePrice" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="psix_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOtherWeightedAverageExercisePrice" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOtherWeightedAverageExercisePrice" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="psix_SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionEquityInstrumentsExercisesInPeriodWeightedAverageExercisePrice" abstract="false" name="SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionEquityInstrumentsExercisesInPeriodWeightedAverageExercisePrice" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="psix_SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionEquityInstrumentsForfeituresInPeriodWeightedAverageExercisePrice" abstract="false" name="SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionEquityInstrumentsForfeituresInPeriodWeightedAverageExercisePrice" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="psix_SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionEquityInstrumentsExpirationsInPeriodWeightedAverageExercisePrice" abstract="false" name="SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionEquityInstrumentsExpirationsInPeriodWeightedAverageExercisePrice" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="psix_SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionEquityInstrumentsExercisableWeightedAverageExercisePrice" abstract="false" name="SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionEquityInstrumentsExercisableWeightedAverageExercisePrice" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="psix_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageRemainingContractualTermAbstract" abstract="true" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageRemainingContractualTermAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="psix_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisableWeightedAverageRemainingContractualTerm" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisableWeightedAverageRemainingContractualTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="psix_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueExercised" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueExercised" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisableAggregateIntrinsicValue" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisableAggregateIntrinsicValue" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="psix_SWIECMember" abstract="true" name="SWIECMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_KNAMember" abstract="true" name="KNAMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_MORAgreementFeeMember" abstract="true" name="MORAgreementFeeMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_DevelopmentCostsReimbursementMember" abstract="true" name="DevelopmentCostsReimbursementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_LongTermPurchaseCommitmentMinimumTargetPeriodForRenewal" abstract="false" name="LongTermPurchaseCommitmentMinimumTargetPeriodForRenewal" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="psix_OtherCommitmentFeeAsAPercentageOfGrossRevenue" abstract="false" name="OtherCommitmentFeeAsAPercentageOfGrossRevenue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="psix_MTLManufacturingEquipmentInc.Member" abstract="true" name="MTLManufacturingEquipmentInc.Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
</xs:schema>
